Abstract: The SVM needs to use approximation accuracy ε, however the LS_ SVM doesn't need ε.According to this characteristics, the paper studied the fitting and generalization capabilities of models that LS_ SVM and SVM established for the penicillin fermentation process respectively.An improved GA selected the parameter values for LS_ SVM and SVM respectively.The experiment shows that the model based on LS-SVM possesses the strong capabilities of fitting and generalization.If ε is too large, the capabilities of fitting and generalization of model based on SVM are not high;if ε is too small, the capabilities of fitting and generalization are relatively high, but the modeling process demands long time.Therfore, the LS_ SVM is more suitable for modeling in fermentation processes.