Pressure release device of closed space of deep water oil and gas well casing pipe

The invention discloses a pressure release device of a closed space of deep water oil and gas well casing pipe and a completion well body structure of the deep water oil and gas well. The pressure release device comprises a main body capable of fixedly installing on the outer wall of a sleeve pipe; the main body is provided with a cavity leading to the inner part of the sleeve pipe; an overflow channel for connecting the cavity with the closed space is arranged on the main body; an elastic piece, a valve body and a valve base are arranged in the cavity; the valve body blocks the valve base under the effect of the elastic piece; the elastic piece applies an initial starting pressure to the valve body; when the pressure of the valve body in the closed space is more than the initial starting pressure, the valve body opens the valve base, thus the closed space is connected to the inner part of the sleeve pipe; when pressure of the valve body in the closed space is less than the initial starting pressure, the valve body blocks the valve base, thus the closed space is not connected to the inner part of the sleeve pipe.