A tapping mode atomic force microscope includes a sinusoidal signal generator. The sinusoidal signal generator generates sinusoidal wave signals to a modulating laser diode for outputting a pulsed laser beam. The laser beam reflects from the back side of a photo detector and then a current signal with a corresponding intensity is output b y the photo detector. Then, the signal is converted by a current to voltage converter and then is operated by a differential amplifier. After the DC component and the undesired multiple frequency harmonics of the current signal is filtered by a band pass filter, the current signal is processed by a demodulation circuit and a low pass filter to produce a voltage value corresponding to probe deformation. After inputting this voltage value to a Z-axis servo controller, a corresponding control command is acquired based on a control algorithm so as to keep the value of the probe deformation constant. If the position of the Z-axis is recorded at a specific time point and all the data are collected, the surface profile of the test sample can be obtained.