The invention discloses a parameter identifiability judgment method for a generator excitation system and relates to judgment of parameter identifiability of the generator excitation system. The parameter identifiability judgment method includes steps of judging relevance parameters by setting up a parameter time domain flexibility matrix, classifying the parameters to be identified into a well-conditioned parameter set and a bad-conditioned parameter set, taking the smallest value of the sum of simulated-frequency-domain flexibility in the bad-conditioned parameter set as a valuation representative, valuing the valuation representative with an empirical value and identifying parameters of the corresponding well-conditioned parameter set. The parameter identifiability judgment method has the advantages that accuracy and stability of parameter judgment results of the generator excitation system are improved, safe and stable operation of the power system is benefited, and the parameter identifiability judgment method has higher engineering practice value.