Abstract: Many methods can be used to determine smoothing parameters in semiparametric model,but smoothing parameters vary with these methods for the same model.After comparative analysis of the L-Curve,GCV(Generalize Cross Validation) and virtual observational approach,the factors influencing smoothing parameter are studied by simulated example.Smoothing parameters have a close relation with signal-to-noise ratio.When the signal-to-noise ratio increases,variation trend of smoothing parameters is different.The best method determining smoothing parameters in different situations is different.