The invention provides a 
motor speed control method, which comprises the following steps: when temperature in a closed housing provided with an electronic 
system is lower than a first critical temperature, the motor is operated under a none-fan 
operation mode, wherein, the speed of the motor under the mode is zero; when the temperature in the closed housing provided with the electronic 
system is higher than the first critical temperature and lower than a second critical temperature, the motor is operated under a mute 
operation mode, wherein, the speed of the motor under the mode is a fixed speed; and when the temperature in the closed housing provided with the electronic 
system is higher than the second critical temperature, the motor is operated under a cooling 
operation mode, wherein, the speed of the motor under the mode is the function of the second critical temperature, and moreover, the speed of the motor is operated between a maximum speed and the fixed speed. The 
motor speed control method can save energy, reduce 
noise, improve 
power loss and increase power efficiency.