The invention discloses a diesel and methanol dual-fuel system of an internal combustion locomotive engine and a method. The dual-fuel system comprises a diesel engine and further comprises a methanolsupplying system, a methanol sprayer assembly and a methanol spraying control system; the methanol supplying system comprises a methanol tank, a methanol filter, a methanol pump, a methanol flowmeter, a distribution box and a methanol pressure-limiting valve, and the methanol tank is sequentially connected with the methanol pump, the methanol flowmeter and the distribution box through pipelines;the distribution box comprises an input end and a plurality of output ends, and each output end is sequentially connected with the methanol pressure-limiting valve and the methanol sprayer assembly through pipelines; the methanol sprayer assembly comprises a methanol rail, a methanol rail pressing plate, a methanol spraying nozzle and a gas inlet bent pipe; and the methanol spraying control systemcomprises a methanol electronic control unit, a control wire harness, an upper computer, a rotating speed sensor, a coolant temperature sensor, a throttle position sensor, a methanol liquid level meter and a fault alarm device.