Abstract: A speed control method of direct current motor fans is revealed. The method used for starting and speed adjustment of the DC motor fan according to a temperature signal includes the following steps. First using a first voltage to start a DC motor fan during a start period and the first voltage is larger than the lowest voltage required for keeping the DC motor fan rotating. Then provide the DC motor fan with the lowest voltage which keeps the DC motor fan rotating during a low-load period after the start period. When a temperature represented by the temperature signal reaches a preset heat dissipation temperature range, a working voltage is adjusted proportionally and linearly according to the temperature signal for speed adjustment of the DC motor fan. The present method has advantages of high starting torque, noise cancellation, energy-saving, and low cost.