Abstract: On the basis of N(S-S 0) m=C , according to the maximum likelihood principle, the formulas of P S N curves are presented which were determined by the single spot method, the single spot group method and the group method.The comparative test was made, and the test data are analyzed and treated. It was found that the P S N curves determined by these three methods were approximate.By means of the single spot method,many specimens may be saved, so the single spot method may be used to determine the P S N curves of the structure components.

Key words: single-spotmethod, single-spot-group method, group method, P-S-N-curve the maximum likelihood principle