Abstract: The characteristics of high temperature, high salt and wide well spacing in Bohai SZ36-1 oil field request good shear stability of injected polymer. Under reservior conditions, a.study was carried out on how the ion (including Na+, K+, Ca2+ and Mg2+) affected viscosity shear retention rate of associating polymer AP-P4 solution. It is found that the key element is Ca2+ and Mg2+ in the solution. Existence of Na+ and K+ can enhance shear retention rate when concentration is 10,000mg/L. Viscosity shear retention rate starts obviously to reduce when concentration of Ca2+ and Mg2+ is 400mg/L ,while Ca2+ and Mg2+ can enhance shear retention rate when concentration is 100 mg/L. Simulating water quality of the water source well A15 in the Bohai SZ36-1 oil field, it has been confirmed that Ca2+ and Mg2+ in the solution are the key factors to affect the viscosity shear stability of association polymer AP-P4.