The invention discloses an engine tail gas treatment system and an engine tail gas treatment method. According to the method, before catalysts in a catalytic converter are not activated, tail gas is not exhausted to the atmosphere air, and after the catalysts are activated, the tail gas is fully catalyzed through the catalytic converter and then is exhausted to the atmosphere air. The system comprises a first three-way valve, a second three-way valve, a third three-way valve and an electromagnetic stop valve. The electromagnetic stop valve is arranged on one side, close to the catalytic converter, of a tail gas pipe; one exhaust port of the first three-way valve is communicated with one air inlet port of the second three-way valve, and the other exhaust port of the first three-way valve is communicated with the other air inlet port of the second three-way valve; one exhaust port of the second three-way valve is communicated with an air inlet of the catalytic converter, and the other exhaust port of the second three-way valve is communicated with an air inlet of an engine; an exhaust opening of the engine is communicated with an air inlet port of the third three-way valve; and one exhaust port of the third three-way valve is communicated with the air inlet of the catalytic converter, and the other exhaust port of the third three-way valve is communicated with the corresponding air inlet port of the second three-way valve.