Abstract: Cold start tester is set up in and an experimental study on the stop and restart of Daqing crude oil is carried out in the laboratory. By changing the water ratio of crude oil and the concentration of the flowimprover, through different condensing period, the curve of cold start gradient & condensation time and the curve of cold start gradient & flow improver concentration are obtained. The effect of condensing time, water content ratio, flow improver concentration and pipeline diameter upon the pressure gradient in cold start are analyzed. The test results and analysis show that adding flow improver of DODE series with different concentration can reduce the cold start pressure gradient and the best concentration of flow improver is 200 mg/L.