The invention provides a stress test method used for an oil well casing. The test method comprises the following steps that S1, the oil well casing arranged in a formation is subjected to selection of test well sections, and holes are drilled in the selected test well sections to form perforation well sections; S2, water is injected into the perforation well sections, and the instantaneous closing pressure Ps of rocks in the corresponding positions of the perforation well sections is tested after water injection is stopped; S3, after water in the perforation well sections is drained, water is injected into the perforation well sections again, and the fracture reopening pressure Pr of the rocks in the corresponding positions of the perforation well sections is tested; and S4, computing is conducted according to the instantaneous closing pressure and the fracture reopening pressure, and the maximum horizontal principal stress sigma Hmax and minimum horizontal principal stress sigma Hmin of the rocks in the corresponding positions of the perforation well sections are obtained. Through the stress values, the optimal steam injection pressure of shallow ultra-viscosity oil reservoirs is effectively determined, and then the steam injection efficiency can be effectively improved, and the heat loss of steam is lowered.