An analysis model has been derived on the vibration of fuel rods in a pressurized water reactor fuel assembly, which is induced by crossflow into the reactor core through a baffle gap. The distribution of speeds of fluid gushing out from a narrow slit onto the fuel rods arrayed in a lattice were first measured and then the force of fluid on fuel rods from an experiment using a mock-up. The force on fuel rods was fitted out using parameters that describe rod position. The amount of energy a fuel rod receives from the fluid through one cycle of its vibrations was calculated as a positional integration of the fluid force. The vibration mode of the fuel rod and the effective momentum flux of the fluid were calculated using the energy. The result of analyzing the effective momentum flux agrees well with the measured result, demonstrating the adequacy of the analysis model developed.