The invention discloses a glass fiber reinforced plastic mortar pipe wall cross section hydraulic pressure sealing performance test device and method. The device comprises a front fixed disc and a rear gland; one side, positioned close to the rear gland, of the front fixed disc is provided with a pipe outer wall positioning ring and a pipe inner wall positioning ring; one side, positioned close to the front fixed disc, of the rear gland is provided with a pipe inner wall installation ring; a sample pipe ring to be detected is arranged between the pipe outer wall positioning ring and the pipe inner wall installation ring in a sealed manner; the sample pipe ring to be detected, the pipe outer wall positioning ring, the pipe inner wall positioning ring and the front fixed disc form a sealed hydraulic pressure detection cavity, the front fixed disc is provided with a water inlet pipe and a water outlet pipe, and a pressure detection meter is mounted on the water inlet pipe. The device and method disclosed in the invention can be used for detecting water tight performance of a pipe cross section of a glass fiber reinforced plastic mortar pipe; the device and method can be used for evaluating pipe manufacture technologies, detecting products and determining an application pressure grade; convenience of quality control of a manufactured glass fiber reinforced plastic mortar pipe can be realized.