In-water self-explosion car roof

The invention discloses an in-water self-explosion car roof which comprises front columns, middle columns, rear columns, upper edge beams and a top cover, wherein a fixing frame is arranged between the upper edge beams and the top cover; bolt fasteners are arranged at the top surfaces of the upper edge beams; bolt lugs are arranged at the periphery of the bottom surface of the top cover; the fixing frame penetrates through the bolt lugs to be connected with the lower part of the top cover in a sleeving manner; bolt hooks matched with the bolt fasteners are arranged at the bottom surface of the fixing frame; a piston cylinder and two reinforcing members are arranged at the bottom surface of the top cover; the piston cylinder is internally provided with a piston; an explosive is arranged between the piston and the piston cylinder; the ends of the two reinforcing members are respectively and fixedly connected with the two ends of the fixing frame of which the hooking direction is opposite to those of the bolt hooks; the other ends of the two reinforcing members are connected with the piston; water level sensors are arranged on the front columns, the middle columns and the rear columns; and each water level sensor comprises an insulation tube and two electrodes. The in-water self-explosion car roof further comprises a back-up power supply, a transmitter and an initiator, wherein the transmitter and the initiator are connected with the back-up power supply, and the water level sensor, the transmitter, the initiator and the piston cylinder are sequentially connected in series. The in-water self-explosion car roof is reasonable in structural design and low in cost, and enables a car to open an escape channel for a driver when the car falls into water.