The distribution of grain in the flight elevator is an important factor affecting the grain mass flow measurement error of photoelectric sensors. To improve the grain mass flow measurement accuracy of combine harvester, a grain thickness measurement method based on infrared photoelectric effect was proposed. The sensor was mainly composed of laser emitter, silicon photocell and signal processing circuit. The nearinfrared light with wavelength of 850~980nm was generated by using the laser emitter, and the light intensity passed through the grain was received by using the silicon photocell. Then, the grain thickness can be acquired according to the variation of received light intensity. An I/V conversion circuit based on T-type feedback network was designed. The Gaussian regression equation was established to describe the relationship between the output voltage and the grain thickness. The effects of laser emitter power, infrared wavelength and rice variety on the sensor measurement performance were analyzed. The results showed that the optimal regression accuracy was received with the infrared wavelength of 940nm, and the measurement error of grain thickness was less than 0.5mm. The measurement range was increased with the increase of laser emitter power. The effective measurement range of about 50mm could be achieved when the power was 500mW. The transmission capacity of infrared ray to grain was increased with the increase of wavelength and decreased with the decrease of grain moisture content. The proposed measurement method and sensor of grain thickness can be used to measure the time interval which grain blocked the light path during the lifting process, and also can be used to analyze the grain distribution in the flight elevator. The research result provided important reference for improving the grain flow measurement accuracy.