Abstract: It was impossible to get standard specimen due to sampling condition. Then nonstandard small specimen should be designed to test performance of the material. The small specimen was designed to test S-N curve in high frequency fatigue test machine PLG-100C. After discussing two problems of the experiment,the key results were as followed: specimen with small section size which was not accorded with GB/T 3075-1982 could be tested in high frequency fatigue test machine PLG-100C effectively;the transition clamping designed meet the test request of small specimen in high frequency fatigue test machine PLG-100C.