Abstract: Since the associative polymer has different solution viscosity forming mechanism with that of HPAM. In this paper, in order to analyze the viscosity loss caused by mechanical shear during associative polymer oil-displacement agent injection allocation process, the effects of mechanical shear on associative polymer solution are studied by combining dynamical laser scattering method, pyrene fluorescence probe spectrometry and atomic force microscopy （AFM）. Studies show that the apparent viscosity, viscosity-average molecular weight and hydrated particle dimension of associative polymer solution decease obviously at the very start of mechanical shearing action. With the increasing of shearing action, numbers of association particles during micro area in the solution is decreasing, but appears slightly recovery after the solution was placed 24 hours, never restores to the previous state. The number of micro-association-area is reduced with the increase of shearing time. Through AFM, the network structures are observed both in the associative polymer solution before and after shearing action and also observed that the hydrated particle dimension and the connections between the particles degrade after shearing. It can be concluded that both the associative polymer molecular chains and association structures damage in the course of shearing action, and because of difficulty of recovery, solution viscosity is fall.