The invention provides a method of measuring the thickness of a thin film. The method comprises the following steps: S1, a neutron beam is used to irradiate a to-be-measured thin film, wherein a firstsurface layer containing 10B or 6Li is arranged on the thin film, the neutron beam is incident from the first surface layer, and the energy spectrum of emitted alpha or 3H particles generated by a 10B (n, alpha)7Li or 6Li (n, alpha)3H reaction is measured; and S2, with the energy spectrum of the emitted alpha or 3H particles obtained through measurement in the first step, the initial energy of the alpha or 3H particles and the energy when the alpha or 3H particles leave the surface of the thin film are obtained, and the thickness of the thin film is calculated and obtained.