The efficiency of hydrophobic associating polyacrylamide ( HAP) used for polymer flooding is determined by its microstructure. The study on analysis means of the microstructure can contribute to screening good functional polymer systems for EOR. The atomic force microscopy (AFM) and scanning electron microscope (SEM) are used to observe the microstructures of HAP solutions at different concentrations

while dynamic light scatter (DLS) and AFM are used to analyze particle size distribution. The DLS results show that as the concentration increases particle size is larger and double peaks appear; the relatively loose network with weak salt resistant ability is replaced by dense network structure that is less susceptible to salt. Both the particle size by DLS and the microstructures can be measured by the AFM at the same time. The comparisons of three means at various solution conditions provide comprehensive characterization revealing the relation of structure and properties of HAP.