Aiming at the problem that the surface shape of polishing pad in continuous polishing is difficult to control precisely, the basic model of optical element polishing is established based on Preston equation and Winkler assumption. Through theoretical analysis, computer simulation and experiment, system characteristics of the continuous polishing is studied further. The result shows that the system has a state that can keep the surface shape of the disk unchanged. The state of this situation is the equilibrium state of the system. It is possible to obtain the high precision plane continuously without adjusting the position of conditioning plate when the workpiece is polished in the equilibrium state. Under different working conditions, the position of the conditioning plate is different in the equilibrium state of the system. The relationship between the position of the conditioning plate and the size of the workpiece in the equilibrium state is quantitively studied by using established model. The experiments prove that the accuracy of workpiece surface shape and processing efficiency are improved when the workpiece is polished in equilibrium state.