The present invention provides a method and system for electrolyzer diagnosis based on curve fitting analysis and efficiency optimization. The present invention relates to monitoring the electrochemical cell components by using curve fitting and estimating the overall electrolyzer performance by using predictive models. The system according to the present invention includes an extraction unit for selecting suitable operation zones, a filtering unit, a curve fitting unit performing linear or non-linear regression by using user-defined equations applied to current-voltage data points and a curve fitting goodness analysis unit. The zones are defined as start-up zones, shutdown zones and load change zones. The system further includes a curve fitting parameters characterization unit for classifying curve fitting parameters by respect to the electrolyzer cells components technology and reference values, and a characterization database for storing fitting coefficients and their characterization.