The invention relates to a microstep subdivision driving control method and circuit of a fixed-frequency PWM full-bridge motor. The microstep subdivision driving control method comprises the steps offirstly, dividing natural step of a stepping motor used by a solar sailboard driving mechanism to microsteps; secondly, allowing a D/A conversion circuit of a control circuit to generate a stepping motor winding current reference sine and cosine signal and a microprocessor to generate a phase sequence signal, and sending the reference sine and cosine signal and the phase sequence signal to a driving circuit so that the two-phase winding of the stepping motor is approximate to step wave currents of a sine function and a cosine function and a low-speed rotation magnetic field is further generated in the motor; and finally, combining the reference sine and cosine signal and sawtooth wave of a fixed frequency, further modulating the current to a PWM control signal, and completing microstep subdivision driving control of the fixed-frequency PWM full-bridge motor.