In order to solve the problems of complex operation, heavy workload and toxic when measuring the grain volume by the existing pycnometer method, the research on accurate measurement of single grain volume draining method was carried out. Combining the image processing technology and the volumetric principle of the liquid draining method, the device was mainly composed of a standard white light source, a linear CCD, a measuring container, a cereal dedicated holding device, a computer and the like. Firstly, the standard white light source was adjusted, the image acquisition environment was enhanced, volume calibration was performed, and the actual volume value V0 was calculated, which was about 0.0023mL represented by a single pixel. Secondly, the liquid level image of measuring vessel was aquired by high accuracy linear CCD camera. Finally, the difference method was used to extract the image of the liquid level change;the number of pixels contained in this part of the image was counted, combining with the volume calibration results to calculate the volume value. Volume draining method and pycnometer method were used for the same batch of cereals respectively. Two sets of volume data were then obtained. Volumetric discharge took 12min, and pycnometer method took 124min. The two groups of data were tested by using the Grubbs test, F test and t test for significant differences tests, and the calculated test values were (TA,TB), FAB, tAB. The values were compared with the critical value of their distribution table: (TA,TB)<T0.05,100,FAB<F0.025(99,99), tAB<t0.05,198, and all of which met the inspection requirements. The results showed that there was no significant difference between the two sets of volume data. The accurate measuring device and method of volumetric discharge of single grain can quickly and precisely measure the volume of irregular single grain, and provide reliable grain volume for scientific research and actual production data.