Abstract: The tensile strength of 304 stainless steels with different chemical compositions was investigated at different environment temperatures and with different tensile rates, and the martensite contents of each stainless steel were also measured before and after tensile test. The results indicate that when the tests were carried out under the temperature and rate ranges prescribed in the standard of tensile test method at room temperature — GB/T 228.1-2010, the measured tensile strength of 304 stainless steels was mainly influenced by environment temperature. And when the environment temperature fluctuated between 10 ℃ and 35 ℃, the measured tensile strength might have a difference about 120 MPa. Under the condition of lower environment temperature and test rate, the higher the TMd30 value of 304 stainless steel was, the easier the martensite transformation was, which induced a rapid increase of tensile strength.