The invention discloses a coal seam gas parameter while-drilling testing method and device which are suitable for coal seam gas/coal bed methane parameter while-drilling tests, gas extraction effect evaluation and the like. By means of while-drilling testing hole bottom gas and coal seam information, while-drilling tests anywhere of the coal seam gas parameters are achieved. The device comprises a cabin body, a pressure sensor, a temperature sensor, a flow sensor, an acoustic emission sensor, a monitoring and controlling module, a power module and a communication module, and the device is arranged between a drill bit and a first drill stem. In a hole drilling process, the temperature sensor can monitor a temperature at a measurement point in real time; in a drill stopping period, a hole is sealed to form a pressure measuring chamber, and a pressure sensor can monitor gas pressure in real time; after pressure testing is finished, the flow sensor can monitor drill hole gas discharge in real time; coal seam gas pressure, a gas content and an initial desorption gas amount at the measuring point can be comprehensively calculated out. The coal seam gas parameter while-drilling testing method and device disclosed by the invention can test and calculate coal seam gas/coal bed methane parameters while drilling and anywhere and have the advantages of no sampling, while-drilling test anywhere, multi-parameter synchronous test and the like.