The invention discloses a formula car engine air intake system, which comprises an air filter, a throttle valve, a flow limiting opening, a diffusion tube, a resonant cavity, a variable air intake manifold and a manifold length regulator, wherein the inlet cone angle and the outlet cone angle of the flow limiting opening are respectively 14 degrees and 6 degrees, the outlet of the flow limiting opening is connected with the diffusion tube, the outlet of the diffusion tube is connected with the resonant cavity, the diffusion angle of the diffusion tube is 6 degrees, the length is 220mm, the resonant cavity is molded by an ABS material through upper and lower die separating and numerical control milling, the volume is 3L, and the internal part of the resonant cavity is equipped with the manifold length regulator. The working length of the air intake manifold is enabled to meet manifold characteristic requirements that the air intake manifold needs to be thin and long at a low speed and needs to be short and thick at a high speed of the engine through additionally arranging the manifold length regulator, the variable length of the air intake manifold can better utilize a resonant airintake effect of the engine in different speed ranges, the air intake efficiency is improved, and the overall performance of the variable air intake manifold is better than that of the traditional non-variable air intake manifold structure.