Silo is widely used in grain, logistics, electric power, metallurgy and other industries. Therefore, the reasonable design of silo structure is the key. China is a large country of grain production, with application of the modern granary environmental protection, energy saving, green and other concepts, the cylinder wall is higher, and larger diameter, occupies less land, saves resources of the silo and is more and more in line with the future development trend of granary, and with the trend of rapid development around the world. With the increasing height and diameter of silo, the problem of failure in silo discharging is becoming more prominent. The dynamic lateral pressure of grain silo during discharging is the major cause of silo failure. In this paper, based on the indoor grain silo discharging model test, the whole process of the silo center emptying was recorded with high-speed camera, the flow pattern of grain was analyzed with image processing technology, and the dynamic pressure generated during the discharge process was measured. Based on this test, the particle flow code (PFC3D) was used to carry out numerical simulation to track the movement of specific particles in the test. By comparing the results of the experiment and the numerical simulation, the mechanism of overpressure in the discharge of the silo was explored. Through this study, in the process of discharging in the center, there were two kinds of flow states, the mass flow and the tubular flow. At the beginning of the discharge, the stored material flowed as mass flow. After a period of time, the upper part of the material flowed as mass flow, the bottom of the storage was a tubular flow, and the mass flow was in the high diameter ratio close to 1 of the height position to convert to tubular flow. When the discharging height reached 1.1m, the stored material flowed in tubular flow until the discharge was completed. Both the dynamic lateral pressure and the static lateral pressure increased with the depth of the measuring point, and the dynamic lateral pressure was greater than the static lateral pressure. At the beginning of the discharge, the dynamic lateral pressure measured by the silo suddenly increased, and then the dynamic lateral pressure value decreased with the continuous reduction of the storage height. The overpressure coefficient measured by the three groups of sensors was larger in the height range of the high diameter ratio close to 1, and the overpressure phenomenon was obvious. In the process of silo discharging, the speed of tubular flow of the bottom stored material was greater than the speed of the mass flow of the middle and upper stored material. There was a pressure arch at the junction of the two flow states, and the existence of the pressurized arch hindered the normal flow of the upper stored material, which led to the self-weight of the stored material and the additional force caused by the change of momentum was almost entirely by the arch, resulting in the increase of the dynamic lateral pressure and a significant overpressure phenomenon. [ABSTRACT FROM AUTHOR]