The invention discloses a coal seam gas parameter detection device based on dead space pressure conversion. The coal seam gas parameter detection device comprises a simulation chamber and a simulationregulator, a sampler is arranged in the simulation chamber; an exhaust pipe at the fixed end of the sampler is connected with one end of a first three-way pipe through a first conduit, and an exhaustvalve is arranged on the exhaust pipe; the sampler is arranged on a weighing tray of the quality detector; the rest two ends of the first three-way pipe are respectively connected with a pressure gauge and a second conduit, the second conduit is connected with one end of a second three-way pipe, and the rest two ends of the second three-way pipe are respectively connected with an exchange air pipe and a vacuum air pipe which penetrating the simulation chamber; and the second conduit, the exchange air pipe and the vacuum air pipe are respectively provided with a first air valve, a second air valve and a third air valve. The coal seam gas parameter detection device achieves the accurate measurement and calculation of the coal seam gas pressure and the coal seam gas content, and implementation of safety measures of a mine is facilitated. The gas content can be estimated, so that the gas yield is determined. The labor cost and the time investment can be reduced.