The invention provides a safety operation system for combustible gas at a wellhead based on adjustable annular suction and assisted discharge. The safety operation system comprises a sand draining pipeline, adjustable annular suction and assisted discharge mechanisms, an ignition device, a gas injection unit and a first gas injection manifold, where the wellhead is connected with the sand drainingpipeline by means of the adjustable annular suction and assisted discharge mechanisms; inert gas is generated by the gas injection unit; the first gas injection manifold provides the inert gas generated by the gas injection unit for the adjustable suction and assisted discharge mechanisms to form a negative-pressure suction effect; and the ignition device is arranged at an outlet end of the sanddraining pipeline and can ignite the combustible gas drained by the sand draining pipeline. The safety operation system can realize dual-channel suction and gas injection adjustable nitrogen injectionsuction way, eliminates safety risk that natural gas overflows from the wellhead, which is caused in the well opening operation such as pipe trip and rubber core replacement under the condition thata small amount of natural gas occurs in the stratum, remarkably improves the field operation safety, is beneficial for taking advantages of gas drilling speed increase, and is applied in a counterflush drilling field.