Flow regime in the bulkhead gate slot is very complex and the slot is easily damaged because of flow cavitation. We investigated the variation regularity of flow regime, pressure, and cavitation number of the segment near the gate slot through hydraulic model test. The emptying tunnel of Kajiwa Hydropower Station was taken as a case study. Results showed that pressure-flow segment behind the gate could improve the flow regime. When the gate was fully open, no negative pressure appeared in each area, and the possibility of water cavitation was rather low. When the gate was partially open, negative pressure was found in the gate slot and the segment behind the gate, with peak negative pressure on the floor of the gate slot, and high possibility of water cavitation. The water fluctuation was featured by large amplitude and low frequency, which was the characteristics of strong turbulent flow. The results could provide reference for the slot design of high-head deep-hole bulkhead gate.