The utility model discloses an exhaust emission by-pass governing system of an engine and aims at overcoming the problem that a by-pass exhausted air quantity can not be accurately controlled in the prior art. The exhaust emission by-pass governing system of the engine comprises the engine, a turbine, a compressor, an air intake pressure sensor, a discharge pressure sensor, an exhaust by-pass magnetic valve, a by-pass controller, an engine speed sensor, an accelerator pedal position sensor and an air flow meter. The air intake pressure sensor and the discharge pressure sensor are arranged on an intake manifold and an exhaust manifold of the engine. The discharge by-pass magnetic valve is connected between the exhaust manifold of the engine and a turbine back exhaust pipe of the turbine. The air flow meter is connected on an air inlet pipe of the compressor in series. A signal input end of the exhaust by-pass magnetic valve is connected with a signal output end of the by-pass controller through wires. The air intake pressure sensor, the exhaust pressure sensor, the engine speed sensor and a signal output end of the accelerator pedal position sensor are connected with the signal input end of the by-pass controller through wires.