The invention discloses a power system of an electric automobile. The power system comprises a generator, a power cell, a power cell management machine, a starting machine, a bidirectional DC/DC converter, a starting cell, and a starting cell management machine, wherein the power cell is used for providing electric energy for the electric automobile; the starting machine is used for starting the generator; a high-voltage end of the bidirectional DC/DC converter is connected with the power cell; the starting cell is connected with a lower-voltage end of the bidirectional DC/DC converter and is used for supplying electricity for the starting machine; the starting cell management machine is used for detecting the temperature of the starting cell, and when the temperature of the starting cell is lower than a preset temperature, the starting cell management machine controls the bidirectional DC/DC converter, so that the starting cell discharges to the power cell. According to the power system disclosed by the invention, the striking capacity of the complete automobile under the ultralow temperature environment can be improved, the cost does not need to be increased, and the occupied space of the cell does not need to be enlarged. The invention further discloses the electric automobile comprising the power system of the electric automobile and a starting method of the electric automobile.