Abstract: The laser induced fluorescence method, as a new technique in the field of visualization experiment field, has received more and more attention to the nuclear reactor thermal-hydraulic research. The laser induced fluorescence method was applied in the measurement of void fraction of gas-liquid two-phase flow. The principle of the void fraction measurement based on laser induced fluorescence method was introduced, and the detail procedure of this measurement technique was described, then the method of picture image data processing was presented to get the void fraction information. An experimental investigation based on planar laser induced fluorescence was conducted to measure the void fraction in vertical rectangular pipe. By comparing the void fraction measured by the laser induced fluorescence method with the theoretical analysis result, it is found that the void fraction fits well with the predicted value. Therefore, the laser induced fluorescence method can be well applied in the continuous measurement of void fraction, with which the flow field will not be disturbed.