Diffuser can improve the performance of tubular pump to a certain extent. Three dimensional laser Doppler velocimetry (3D-LDV) technique was used to measure the flow field in guide vane of tubular pump, and the velocity distribution inside the diffuser was obtained. The circumferential velocity gradually decreased from inlet to outlet, the axial velocity distributed like U-shaped, the velocity close to the wall was low, and the velocity of middle area was relatively high, the radial velocity distribution velocity was also relatively high speed. The flow field between experimental and numerical results agreed well with each other. It showed that the distribution of circumferential velocity and axial velocity were similar, but the radial velocity deviation between the LDV results and the CFD ones was big.