Aiming at the problem of data lacking for internal dynamics in landslide surge tests, an improved particle image velocimetry technology was used to build a landslide surge test platform.A viscoplastic material called Carbopol was chosen as the landslide material. Using fluorescence seeding particles, the internal dynamics of the submerged sliding mass and body of water was obtained respectively, and then the velocity field of the two phases was estimated. Using the velocity field data, the evolution of the mass and mean velocity of the submerged sliding mass, as well as the momentum variation of the sliding mass and body of water were calculated and analyzed. The results show that there is a high correlation between the momentum change trend of landslide and water body and the momentum of landslide body entering water, providing more complex and multivariate data support for the theoretical research of momentum transformation mechanism of two-phase coupling.