The advantages and disadvantages of existing extraction method about planar linkage curve characteristic parameter are analyzed and summarized.On the basis of the property that high-frequency component of the Fourier descriptor can well explain the details,and low-frequency component determines the overall shape of the object boundary,the method by using Fourier descriptor to extract characteristic parameters of the planar linkage curve is proposed,and the numerical atlas database of planar linkage curve characteristic parameter is established.The calculation results show that the low-frequency component of Fourier descriptor can well reproduce the original closed curve through the inverse Fourier transform,and the normalized Fourier descriptor has good robustness,the corresponding numerical atlas database has the advantages of high precision,simple calculation,small redundancy.All of these bring a new thinking way for four-bar linkage curve replay.