Based on light induced thermal effect, all-optical intensity modulation characteristics of optical microfiber coupler (OMC) are studied. The theoretical analysis shows that, the modulation response efficiency of OMC is proportional to the waist length, loss coefficient, and pump modulation intensity, and is inversely proportional to the radius of the OMC waist coupling fiber. In the experiment research, the intensity modulated 980 nm pump light is injected into the OMC to heat the waist region, and the all-optical control function of the 1550 nm working light transmitted by OMC is obtained. The results show that, the OMC can realize intensity modulation with a whole cycle and a large modulation depth under modulation pump power of hundreds of microwatts. In addition, the amplitude of the modulation response signal has a linear response to the amplitude of intensity modulated 980 nm pump light in a low power region. The threshold of the required modulated pump light power is as low as several dozens of micro watts. The research has provide experimental data for the development of all-optical functional devices, such as optical attenuation, optical switch, intensity modulator, and it also provides a reference scheme for the control of the thermal stability of photonics integrated equipment and the security of quantum communication system.