The utility model discloses an engine exhaust emission single-cycle sampling system. The problem that engine single-cycle exhaust emission cannot be separated is solved. The engine exhaust emission single-cycle sampling system comprises a circuit control system, an actuator, an air storage device and a vacuum degree regulation device, wherein the actuator comprises a high-frequency solenoid valve, a compressed air cylinder, a two-position five-way solenoid valve, a crank connecting rod mechanism, a butterfly valve and a high-pressure air source; the left end of the high-frequency solenoid valve is connected with the butterfly valve; the right end of the high-frequency solenoid valve is connected with a rapid joint of the air storage device and a third ball valve of the vacuum degree regulation device; the crank connecting rod mechanism is connected with a valve rod of the butterfly valve; the left end of the crank connecting rod mechanism is connected with the compressed air cylinder; an air inlet/outlet in the left side of the compressed air cylinder is connected with an air outlet pipe on the left side of the two-position five-way solenoid valve; an air inlet/outlet in the right side of the compressed air cylinder is connected with an air outlet pipe on the right side of the two-position five-way solenoid valve; the left end of the high-pressure air source is connected with an air inlet pipe of the two-position five-way solenoid valve; an output end of a solid-state relay of the circuit control system is in wire connection with the two-position five-way solenoid valve and the high-frequency solenoid valve.