The invention discloses an open-loop control method and an open-loop control system of a permanent magnet synchronous motor based on space vector pulse width modulation (SVPWM). To each given stator power frequency, the amplitude of stator voltage corresponding to the given stator power frequency is found through searching a two-dimensional vector table of the stator voltage and the stator power frequency, wherein the two-dimensional vector table is set according to a sectional voltage/frequency ratio curve in advance, that is to say, the ratio of the stator voltage and the stator power frequency in the two-dimensional vector table disclosed by the invention is not a normal value; and the ratio is different in different interval sections. In the prior art, as the voltage/frequency ratio is a normal value, when a load changes, a motor is out of step easily so as to cause overcurrent to the system. In the method disclosed by the invention, the sectional voltage/frequency ratio can guarantee the motor to adapt to the change of the load, reduce the consumption of the motor and improve the efficiency. In a constant power area, phase compensation is introduced, so that weak magnetic control is realized by using the regulated phase, and weak magnetic speed improvement is realized.