To improve detection precision and reliability of the porosimeter for particle materials, a constant volume porosimeter and an automatic control system were developed based on the ideal gas state equation and gas displacement method. In 0.1~0.4 MPa, the results showed that the higher the inflation pressure, the better the repeatability and precision of porosimeter when stainless steel balls, prisms, pebbles and fine stones were used in the test. The equation of error compensation was proposed through the calibration experiment using standard stainless steel balls and cylinders in the standard condition. The porosity of the samples were 16.02%, 25.14%, 35.57%, 49.05%, 58.42%, 67.79%, 76.57%, 85.36%, 94.14% respectively. In the inflation pressure limit of 0.4 MPa, with 13.5% wet basis of paddy porosity, the test results showed that the range of porosity was 0.3%, when filling rates of sample were 25%,50%,75%,100% respectively. The reliability of measurement was proved by the results.