Abstract: Focused on chemical pour point depression (PPD)in wax oil pipeline transportation process, the progress in depression mechanism are reviewed from the microscopic procedure of wax deposition. The influences of pour point depressant on wax deposition are summarized from two aspects in crystallography and thermodynamics. Through crystallography analysis, it is considered that although PPD can not inhibit crystallization process of wax, it can provide more nucleuses to improve the crystal symmetry, break the link between wax crystal by modifying its structure and surface property. Through thermodynamic analysis, it was thought that PPD molecular can provide an easier thermal way for wax crystallization, and make the whole system being a stable state without crystal link. The two aspects analysis and description on depression mechanism can provide a good reference to the molecular design and structural optimization in pour point depressants.