A bogie gas tightness detection device and a detection method thereof relate to the technical field of railway passenger car bogie welding and assembling. The detection device comprises a helium storage tank, a gas power unit, a digital display pressure controller, a gas distribution pipe, a pressure maintaining pipe, a needle valve, a digital pressure gauge, an exhaust valve, and a helium detector. The gas power unit feeds helium in the helium storage tank into the pressure maintaining pipe according to a set pressure. The pressure maintaining pipe offers pipe interfaces of a variety of specifications and models to be connected with a brake pipe. During test, gas of a set pressure is fed into the brake pipe, the reading of the digital pressure gauge is observed, and the needle valve is closed when the pressure reaches a specified pressure value. The helium detector is adopted to detect the brake pipe, and the leakage position is recorded when the detector alarms. The detection device of the invention has the characteristics of small size, low weight and high accuracy of detection. Detection does not rely on an external air source, and the pressure of output gas can be adjusted. The detection device and the detection method are applicable to gas tightness detection under all kinds of requirements.