The invention relates to a method for quickly designing mechanical products based on virtual instruments and reverse engineering. The method comprises the following steps of: acquiring the point cloud data through a prototype product model at first, obtaining a prototype product curved surface model through utilizing an imageware software according to the obtained point cloud data, utilizing CATIA software to form a prototype product solid model of the curved surface model, using a parametrization design to obtain a new product solid model, analyzing and computing the new model through utilizing ANSYS software so as to obtain a new product model which satisfies requirements, and finally, storing the model into a database and quickly forming through a quick forming machine. The method consists of a prototype product model data acquiring part, a data processing, analyzing and managing part with a computation and analysis software and a quick forming part. The data acquiring part is an optical measuring instrument, data measurement and acquisition can be realized through scanning, and the point cloud data of the model can be obtained.