Abstract: In long distance pipeline transportation with depressant at atmospheric temperature, depressant crude oil is subjected to long terms of pipeline flow shear inevitably. Study showed that the pipeline flow shear in slow drop in temperature will produce an evident effect on low temperature fluidity of oil sample, the degree of influence has close relationship with rates of the drop in temperature and times of shear, and there exists an "optimum temperature cooling shear stress". Described a reflection of the optimum temperature cooling shear stress over the changes of depressant crude oil's viscosity and pour point (set point). Study proved that high carbon wax content in oil sample would has influence on medium and low speed shearing effects, and the degree of the effect has close relationship with temperature cooling rate and shearing time.