P-Least Squares (P-LS) method is Least Squares (LS) method promotion, based on the criteria of error -squares minimal to select parameter , namely satisfies following constitute the curve-fitting method. Due to the arbitrariness of the number , P-LS method has a wide field of application, when , P-LS approximation translated Chebyshev optimal approximation. This paper discusses the general principles of P-LS method; provides a way to realize the general solution of P-LS approximation. P-Least Squares method not only has significantly reduces the maximum error, also has solved the problems of Chebyshev approximation non-solution in some complex non-linear approximations,and also has the computation conveniently, can carry on the large-scale multi-data processing ability. This method is introduced by some examples unified in the materials science, the chemical engineering and the life body change.