Ellipsometry is an important measurement tool for thin films. A novel calibration method is described for single wavelength ellipsometry, both theoretically (with simulation) and experimentally. The basic idea is as follows: if the relevant information (refractive index n, absorption coefficient k, thickness d) of samples is given prior to measurements, the system calibrating parameters (angle of polarizer P, angle of analyzer A, offset angle of compensator Cs, phase shift of compensator δ, and angel of incidence θ0) can be deduced from the comparison of the measured and calculated Fourier coefficients, with the least square method. These calibrated system parameters can then be used to measure unknown samples. This method is easy to implement and cost-saving. 2~6 samples have been tested in the calibrations, and the errors are analyzed with simulation. Finally, this method is applied to a realistic 632.8 nm laser ellipsometer, and the results obtained with the new calibration method prove the validity of the method and show a maximum error of 0.26 nm.