The invention discloses a soft start control method and a soft start controller for an electronic fan. In the invention, soft start is realized by a variable duty ratio pulse-width modulation (PMW) wave control power metal oxide semiconductor (MOS) tube consisting of a triangular wave generating circuit, a remote control (RC) charge and discharge circuit and a comparator. A square wave signal u3 can be obtained by computing and designing a triangular wave generation circuit with a fixed frequency and by comparing a voltage u2 with a triangular wave signal u1 serving as a reference; when the voltage value u2 is continuously increased from zero to the peak value of the triangular wave signal u1, the duty ratio of the square wave signal u3 continuously reduces from 100 percent to 0 percent, so a signal of which the duty ratio continuously reduces from 100 percent to 0 percent and is finally stabilized at 0 percent is obtained; and thus, the function of soft start can be realized by usingthe signal to control a power switching tube. The voltage u2 can be generated by the RC charge and discharge circuit, and the time of the duty ratio which reduces from 100 percent to 0 percent can beadjusted by properly regulating the values of matched resistance and capacitance.