Abstract: In order to study the main factors affecting the hydraulic gradient of fly ash paste pipeline transportation, hydraulic test was carried out by the test of transmission ring pipe. We use orthogonal test method to analyze the test results, and determine quantitatively the sensitivity of hydraulic gradient of the fly ash paste on the flow rate, pipe diameter and slurry concentration, and the change trend with different factors. Results show that the hydraulic gradient of fly ash paste increases with the flow rate and concentration, and decreases with pipe diameter, and the flow rate is the main factor that affects the hydraulic gradient. In order to improve the properties of fly ash slurry pump, the A₁B₃C₂ transport scheme is selected, namely velocity of 1 m/s, diameter of 125 mm, and the slurry concentration is 53%.