A Mueller matrix measuring method is brought forward based on nonlinear least squares fitting. Stokes parameters of output polarization state are measured, and functions between output polarization states, the system unknown parameters and sample′s Mueller matrix are built. Nonlinear least squares fitting method is used to calculate sample′s Mueller matrix. Then a Mueller matrix ellipsometer measuring system based on ferroelectric liquid crystal retarders and rotating waveplate and rotating polarizer is established, the Labview software is applied to realize the intelligent. Error analysis and measurement are done. It is found that the Mueller matrix measuring precision of the system is within 0.01 and repeatability is 0.005 in wavelength range 600~900 nm。The measuring system avoids the complex calibration of Mueller matrix ellipsometer as before, simplifying measuring procedures and realizing the self-calibration measurement.