In order to solve the disadvantages of conventional electrical flowmeter resist electromagnetic interference ability, based on the Carmen vortex street and light interference principle, A fiber optic Fabry-Perot vortex flowmeter is proposed for the HVAC system, the flowmeter using the characteristics of the periodic vortex around fluid, the connection between velocity and interferometer output light intensity, with the change of light intensity frequency reflect the flow rate, realize the flow rate sensing. The finite volume method is used to simulate the flowmeter, reasonably select the best detection point, and compare the simulation data with the theoretical value, which proves the rationality and feasibility of the flowmeter design.