The invention discloses an electric generator based on a methanol water hydrogen-making system and an electricity generation method thereof. The electric generator comprises a methanol water storage container, a delivery pump, a heat exchanger, a reformer, a separation device and a fuel cell, wherein the delivery pump is used for delivering methanol and water to a reforming chamber of the reformer; the heat exchanger is used for carrying out heat exchange on the low-temperature methanol and water and a high-temperature mixed gas output from the reforming chamber; the reformer is provided with the reforming chamber and an electric heater, and the electric heater provides heat energy for the reforming chamber; and the high-temperature mixed gas which takes carbon dioxide and hydrogen as main parts is prepared in the reforming chamber, passes through the heat exchanger and then enters the separation device to be separated to obtain the hydrogen, and the hydrogen is delivered to the fuel cell and subjected to electrochemical reaction in the fuel cell to generate electric energy, a part of the electric energy provides electricity for the delivery pump and the electric heater, and the rest of the electric energy is output. According to the electric generator, the reformer has no need of being provided with a combustion chamber, an air inlet fan, an air inlet channel and a smoke window, the heating temperature inside the reformer is easily controlled and stable, and the reformer is simple in structure, stable in operation and low in overhaul difficulty.