In the flood season of 2014, through the joint operation of water and sediment in Wanjiazhai, Sanmenxia and Xiaolangdi reservoirs, the gravity flow of Xiaolangdi Reservoir was shaped and the evolution data of the density flow at the dive site, the reservoir evolution area and the dam front area were measured. In the vertical direction of the submerged point , the analysis shows that the variation of the thickness of density flow synchronizes with the incoming flow, and the average flow velocity gradually increases from top to bottom. In the horizontal direction, the average flow velocity and sediment concentration are larger and the edge flow is smaller. In the evolution area of the reservoir, the thickness of density flow increases along the way in the same day and the height appears near the dam, and the general trend of the average flow rate decreases along the course. In the direction of the incoming flow, the sediment concentration in the front section becomes larger than that in the posterior section. In the vertical direction, when the outlet and the drain hole are opened, the average flow velocity appears two extremums in clear water layer and density flow layer's bottom, with sediment concentration's extremum appearing in the bottom of density current. Through the analysis of the movement of density current in xiao langdi reservoir, it can provide technical support for optimizing the reservoir scheduling ,in order to reduce sedimentation, and prolong the service life of the reservoir.