[Objective] Rock-Filled Concrete (RFC) naturally mitigates thermal cracking due to its low hydration heat and reduced cement consumption, its application in extreme winter conditions remains insufficiently explored. Previous studies have predominantly focused on mild climates or early-stage temperature fields under normal conditions. Through in-situ prototype monitoring of an RFC placement lift during winter construction in cold region, this study systematically evaluates pouring feasibility, determines critical construction control points, and establishes effective temperature control and crack prevention protocols for freezing environments. [Methods] A comprehensive field experiment was conducted at the Hami RFC sediment check dam project in Xinjiang, China. To capture high-resolution real-time data, 20 compactness and 18 temperature sensors were precisely embedded within the placement lift. The monitoring period covered the complete SCC filling process and the early-age curing phase. To evaluate thermal insulation strategies, the study comparatively monitored the internal temperature responses of concrete cured behind standard steel formworks versus precast concrete formworks equipped with built-in insulation layers. [Results] (1)SCC successfully submerged all 20 compactness and 18 temperature sensors, demonstrating excellent filling density and overcoming potential sub-zero temperature viscosity issues. During pouring, the free liquid surface of the SCC exhibited a stable rising slope of 0.066; specifically, for every 6.6 cm increase in liquid height at the pouring point, the leading edge extended exactly 1 meter. (2)Spatiotemporal monitoring revealed that high-temperature gradients were predominantly localized near the anti-seepage layer and free faces, with no significant gradients within the interior of the placement lift. The internal temperature difference within the anti-seepage layer stabilized at approximately 2 ℃, while the overall internal temperature was maintained between 3 ℃ and 5 ℃.(3) Internal curing temperatures remained within a reasonable developmental range. Prior to 40 days of age, the middle region temperature remained above 10 ℃, and the interface between the anti-seepage layer and rockfill stayed above 5 ℃.(4) The peak temperature inside the standard steel formwork was 9 ℃ to 10 ℃ lower than inside the insulated concrete formwork. The precast concrete formwork with built-in insulation demonstrated superior thermal retention, keeping boundary temperatures above 5 ℃ for the crucial first 28 days.(5) Despite three rapid temperature drops and snowfalls within the first month, rigorous surface inspections confirmed the complete absence of surface cracks. [Conclusions] Empirical findings robustly validate the feasibility of executing RFC construction in harsh, low-temperature winter environments without compromising structural compactness or integrity. The study identifies two critical periods requiring stringent temperature control due to high-temperature gradients in the anti-seepage layer: (1) the peak temperature stage, occurring approximately 2 days post-pouring, and (2) periods immediately following rapid temperature drops, particularly within 1 to 4 weeks before internal hydration heat fully subsides. During this latter period, the superimposition of residual stress, caused by the evolving elastic modulus of the maturing SCC, and temperature stress creates high surface cracking risks. To mitigate these risks, implementing robust thermal insulation at free faces is paramount. Utilizing precast concrete formworks with built-in insulation is recommended as a standard construction measure in cold regions. Furthermore, rigorous thermal insulation covering and regular inspections must be mandated for at least one month following the pour. Proactively monitoring environmental temperature fluctuations and applying immediate protective measures during rapid temperature drops successfully prevents the propagation of early-age thermal cracks in cold-region RFC dams.