The application provides a gas accumulation simulation experiment device and an experiment method thereof, and the device comprises the following components: a horizontal wellbore, a gas injection system, a liquid injection pump, a first valve, a first pressure sensor and a liquid flow meter; wherein the horizontal wellbore extends in a wave shape; the horizontal wellbore is provided with an inletand an outlet which are opposite to each other in the extending direction of the horizontal wellbore; the gas injection system communicates with the inlet; the gas injection system is used for injecting gas into the horizontal wellbore; the liquid injection pump communicates with the inlet; the liquid injection pump is used for injecting liquid into the horizontal wellbore; the first valve is arranged at one end of the horizontal wellbore close to the outlet; the first valve is used for controlling the opening and closing of the outlet; the first pressure sensor is disposed between the firstvalve and the horizontal wellbore, and the first pressure sensor is used for measuring the pressure of the fluid passing through the outlet; and the liquid flow meter is arranged between the liquid injection pump and the inlet. The embodiment of the application provides the gas accumulation simulation experiment device capable of revealing the gathering and discharging rule of gas in the horizontal wellbore and the experiment method thereof.