In order to discover the relationship between structure and performance of hydrophobically associating polymer, the effect of the length of the micro block length（N_H） on the rheological properties of the hydrophobically associating polymer，a acrylamide-sodium acrylate-N-Dodecylacrylamide copolymer, containing 0.2 mol% N-Dodecylacrylamide hydrophobic monomer chain，was studied by using the method of steady state stress，shear rate and frequency scanning. The results showed that，with the increase of micro-block length，the associative effect of the polymer enhanced and the polymer solution was easier to form a space network structure，and the critical association concentration（CAC） decreased and thickening performance and viscoelastic properties were greatly improved .When N_H increased from 3.3 to 12.5，CAC decreased from 1684 mg/L to 846 mg/L，and zero shear viscosity increased from 204.73 mPa·s to 65833.19 mPa·s，and relaxation time increased from 0.07 s to 12.64 s. The rheological experiments confirmed that the association and disassociation of hydrophobically associating polymer was a reversible dynamic process，the longer the micro block length，the slower the recovery rate of structural viscosity after shear damage，but the higher viscosity after the recovery. Under the same conditions，increasing the temperature and the ionic strength of the solution was beneficial to enhance the association effect within certain range，which resulted in enhancing the resistance to temperature and salt performance of associative polymer to a higher level.