Drawing the grain yield map during the operation of the combine harvester is a requirement to achieve precision agriculture. To draw the yield map, the grain flow into the grain tank must be measured in real time during the combined harvest. Applying the structured light visual measurement technology to achieve the measurement of grain volume flow was proposed. Ordinary chute was used as the conveyor to measure the volume flow of the grain. Rollers and encoders were used to measure the flow velocity of the grain in the chute. A structured light three-dimensional vision system was constructed based on the principle of laser triangulation to measure the flow valley in the chute cross-section profile of grain. The relationship between the object length and the pixel offset value was established by the test parameter calibration method. Based on the pre-processing of the structured light image, the cross-sectional profile of the grain flow was obtained by the threshold determination method. The trapezoidal micro-element summation method was used to establish the grain flow section calculation model and the volume calculation model. The effects of the chute inclination angle and image acquisition frame rate on the measurement error of grain volume flow were experimentally studied. The experimental results showed that when the chute inclination angle was from 15° to 30° and the frame light acquisition frame rate was from 40f/s to 100f/s, the measurement error of volume flow of the four kinds of grain was no more than 5.2%, the coefficient of variation of repeated experiments was no more than 0.021, and the root mean square error was no more than 1.268L. When the measurement volume was 17.6L, the chute inclination angle was 30°, and the structured light image acquisition frame rate was 100f/s, the minimum measurement error was 0.74%. When the measurement volume was 39.2L, the inclination of the chute was 20°, and the frame rate of the structured light image was 40f/s, the maximum measurement error was 5.2%. A structured light three-dimensional visual measurement system and a trapezoidal micro-element integral summation method were used to establish a grain flow volume calculation model, which can realize the online measurement of the grain volume conveyed by the chute.