When coarse particles such as coarse sand and gravel are transported by dredged pipelines,due to factors such as complex composition of particle size,large fluctuations in concentration and local resistance,it is easy to cause problems such as transportation efficiency,siltation blockage and difficult operation.To realize the safe and efficient transportation of coarse particle materials,the coarse sand with a median particle size of 0.82 mm is taken as the research object.To study the flow pattern,loss of frictional drag,critical velocity and slip ratio(transportation efficiency) of coarse sand,pipeline transportation experiments are carried out under different concentrations and flow rates.According to the requirements of dredging construction,the optimal flow pattern and velocity range are determined.The flow state has the advantages of not being easy block,low wear,high transportation stability and high transportation efficiency.The research results on the characteristics of mud and sand transportation and the method for determining the optimal flow pattern have theoretical reference and application value for the safe,stable and efficient transportation of coarse particles.