A testing method for a fan module is provided. When the fan module is tested, a testing computer sends a testing command to a testing device first. Then, the testing device responds to the testing command and controls the fan module to work in a plurality of rotational speed modes in sequence. The testing device reads an actual rotational speed when the fan module works in one of the rotational speed modes and sends the actual rotational speed back to the testing computer. The testing computer compares the actual rotational speed with a corresponding reference rotational speed value stored in the testing computer, and determines the testing result. Finally, the testing result is shown.