Provided are a method for measuring a mechanical parameter of a multi-layer composite thin film structure, and a device for measuring a mechanical parameter of a multi-layer composite thin film structure, which fall within the technical field of the online testing of material parameters of a micro-electro-mechanical system (MEMS for short). By means of the method, based on the relationship between a first-order resonance frequency of a multi-layer composite clamped-clamped beam and a multi-layer composite cantilever beam and parameters such as a material characteristic and a structure size, an equivalent Young's modulus of each layer of a multi-layer composite thin film structure and an equivalent residual stress of each layer are obtained in one step by means of solving a set of equations, which can satisfy the online testing of a multi-layer thin film material, has a simple test structure and calculation method, and has a higher accuracy.
