Groin dam is one of the commonly used regulation structures in waterway regulation. In practical engineering, it is mostly made of block and stone and has certain water permeability. By combining flume generalized model test and theoretical analysis, the influence of different void size and void ratio conditions on the energy change of dam body section, dam head front end and main flow zone was studied. The results show that the smaller the gap size of pervious groins in the dam body, the less the potential energy of water flow through the loss; The kinetic energy at the front of dam head is inversely proportional to the void size and proportional to the void ratio. In the main flow zone, the influence of void size and void fraction on potential energy is not obvious, but on kinetic energy is obvious. The research results are of great significance to deeply understand the instability mechanism of the actual groin dam and provide technical support for the design and repair of groin dams.