[Objective] Cracks induced by hydration heat and associated temperature stress in mass concrete present a critical technical challenge in ultra-high voltage （UHV） substations. Focusing on typical mass concrete for UHV projects， this study systematically investigates the mechanisms by which the combination of fly ash， slag， and inhibitors affects the hydration heat of cementitious composite systems. [Methods] Using typical mass concrete as a case study， a series of hydration heat tests were conducted to investigate the influence of a composite system incorporating fly ash， slag， and inhibitors on the hydration heat of cement. Based on these experiments， a rational control strategy is proposed. [Results] Incorporating slag powder， fly ash， and inhibitors significantly delays the onset of the accelerated hydration phase and reduces total hydration heat. The inhibitory effect of citric acid exhibits a positive correlation with the dosage of mineral admixtures； specifically， citric acid primarily extends the peak time at lower admixture levels， whereas it induces complete process inhibition at higher concentrations. Nano-zinc oxide effectively mitigates early-stage hydration exothermicity； however， rapid subsequent reactions （exceeding 100 hours） may cause thermal stress concentration within cement-based materials， thereby accelerating the risk of cracking. Consequently， zinc oxide is not recommended for controlling hydration temperatures in mass concrete applications. Furthermore， the synergistic use of slag powder， fly ash， and inhibitors influences nucleation and crystal growth during hydration， resulting in an increase in kinetic parameters while simultaneously reducing hydration rates across all stages （evidenced by decreasing K_NG， K_I， and K_D）. Notably， the combination of tartaric acid and fly ash demonstrates the most pronounced effect， achieving a 97.4% reduction in the peak hydration temperature， which is far superior to the 30% to 50% efficiency of conventional material-based temperature control. Additionally， the control system combining inhibitors， mineral admixtures， and water cooling effectively reduces the temperature gradient to below 8.5℃/m， a performance significantly better than traditional temperature control indices. [Conclusions] The type and dosage of retarders should be determined comprehensively during the construction phase of mass concrete， considering their effects on workability， mechanical properties， and durability. From an economic perspective， although the cost of using tartaric acid is slightly higher than that of traditional methods， its remarkable effectiveness at low dosages significantly mitigates cracking， reduces subsequent maintenance costs， and enhances overall economic efficiency. Therefore， these achievements provide scientific support for mix proportion design and temperature control strategy optimization， offering practical guidance for temperature regulation and crack prevention during the construction of UHV substations.