Gas measurement device for underground gas distribution wellhead of oil well

The invention relates to the field of oil and gas field pumping well metering, in particular to an oil well underground gas distribution wellhead measuring device. Comprising a wellhead constant-pressure depressurization gas collection device, an underground primary precession vortex sand outlet separation device, an underground secondary sound wave cutting diffusion dispersion separation device, an underground three-time gravity separation pump inlet gas distribution device and a ground gas measuring and collecting inlet dry mixed transportation device. The wellhead constant-pressure depressurization gas collection device comprises a sleeve, a wellhead four-way joint, a sleeve valve, a gas distribution connector, a sleeve pressure transmitter, a constant-pressure check valve and a sucking pump. The wellhead four-way joint is installed on a casing pipe, and the gas distribution connector is connected with the casing pipe valve, the casing pressure transmitter, the constant-pressure check valve and the sucking