An engine air inflow filling amount forming system in the technical field of internal combustion engines comprises an intake manifold, a heating pipe, a gasoline supply system and an n-heptane oil supply system. One side of the intake manifold is connected with an engine, the other side of the intake manifold is connected with the heating pipe, an oil sprayer of the gasoline supply system is connected with a first oil sprayer seat, and an oil sprayer of the n-heptane oil supply system is connected with a second oil sprayer seat. In the working process, an inflow temperature is adjusted by applying a heating system; a zirconium oxide thermal insulation layer is sprayed on pipes after a heating device and the inner wall surface and the outer wall surface of the intake manifold, heat loss can be effectively reduced, and the requirements of the engine for a heater are reduced; two groups of oil sprayers are symmetrically distributed at the tail end of the intake manifold, oil beams can be directly sprayed into an air inflow duct high in temperature, thereby being favorable for achieving uniform mixing of fuel and air; and two oil supply systems controls proportion of gasoline and n-heptane in real time and adjusts fuel property. The novel engine air inflow filling amount forming system is reasonable in design and simple in structure.