In order to identify fractal scale parameters of machined surface profile accurately, the precisions of different parameter identification methods, such as power spectrum method, structure function method and variance method, are analyzed and compared. Based on discrete power spectrum function and variance method, a revised method of scale parameter identification is advanced. Results show that, in contrast with other methods, the new method could identify more accurate parameter. Those methods are adopted to identify parameters of machined surface profile. The variation of fractal parameters with surface roughness is studied. Research indicated that the preferred method to identify fractal scale parameter is the revised method; otherwise, significant error may occur in the results of parameter identification.