The fracturing job was one of the effective way to improve hydrocarbon reservoir’s permeability and raise oil and gas well’s production. In the fracturing operation, the formation and fracturing fluid temperature were coming linear or non-linear changes with the well depth. The Fracturing fluid pressure was also coming non-linear changes with the well depth. The flow fracturing fluid, the static fluid outside the tubular and the fracturing string was selected as objects in this article. The coupling analysis model of the physical field with the temperature field, flow field and stress field was set up. The 1000m model result of the fracturing string was obtained by adopting ANSYS software. The wellhead temperature about the fracturing string and fluid was 20℃. The inner wall temperature was 36.99 ℃. Its outer wall temperature was 50.55 ℃. The fracturing string temperature was 35.47℃ in the bottom of the well. The string model with 1000m was also selected as research objects. The result in the multi-physic and stress field was obtained. The fractional error in the well of head and bottom was respective 3.73% and 5.97%. Wherefore, it had little impact by using stress field to evaluate the casing strength. Bur it had a certain impact on the axial stress and the hoop stress.