Acoustic field distribution in the measuring space of ultrasonic volumetric flowmeter is mainly determined by the performance of the transducer and the flow field under actual conditions. A hybrid approach combining measured boundary conditions and numerical method was used to predict the acoustic field, in order to solve the problem that only using numerical method has the difficulty in accurately modeling important calculation parameters of actual transducer. The vibration boundary condition of calculation model is accurately obtained by using a laser scanning vibrometer to measure vibration velocity of discrete points on transducer surface and following a data fitting computation, which means that the transducer with the most modelling uncertainty is replaced by the experimental data. The flow fields inside the ultrasonic volumetric flowmeter under different volume flowrates were calculated by computational fluid dynamics, and then the simulation results were inserted into the numerical calculation model as the background field. The acoustic field can be predicted by solving the governing equation derived from linear wave acoustic equations in non-uniform flow with the help of the finite element software COMSOL. The proposed hybrid approach is validated by comparing the predicted and experimental data.