Abstract: In order to more truly react the mechanism of gas-liquid two-phase flow in fluid couplings, the method of CFD(computational fluid dynamics) simulation was used to numerically simulate flow field characteristics in fluid couplings, such as internal flow velocity, pressure and so on, and the technology of PIV(particle image velocimetry) was adopted to test flow field in fluid couplings. The results showed that bubbles in the pump wheel were small and uniform, velocity distribution of pump was regular and increased from inner loop to outer loop; the bubbles in the turbine were more obvious, the turbine came out irregular flow phenomena of vortex, reflux, secondary flow and so on. Flow trend of PIV test and numerical simulation were nearly same. The numerical simulation method of CFD and PIV technology provides effective method to reveal complex flow of the internal flow field characteristics in the hydraulic coupling.