A power system for an electric vehicle, an electric vehicle and a method for charging a power battery are provided. The power system includes: a power battery (10); a charge-discharge socket (20); a bidirectional DC-DC module (30); a driving control switch (40); a bidirectional DC-AC module (50); a motor (M); a motor control switch (60); a charge-discharge control module (70); a battery manager (108); and a control module (80) configured to control the driving control switch (40), the motor control switch (60) and the charge-discharge control module (70) so as to control the power system to enter a charge-discharge mode, and to control the power battery (10) to charge and discharge in a pulse mode so as to heat the power battery (10) when the temperature of the power battery (10) is lower than a predetermined temperature.