The invention discloses an austenitic stainless steel weld-seam ultrasonic detection method, which comprises the following steps that: 1) three weld-seam test blocks which are consistent with a real weld seam to be detected are produced; 2) all artificial reflectors are measured, a reflection strength of overall cross-sectional divided area of the weld seam is obtained through an interpolation method, i.e. a two-dimensional distance amplitude table; 3) size of the divided area in the two-dimensional distance amplitude table is determined, the interpolation is processed firstly according to a same horizontal position; and then the interpolation is executed in the same column, so reflection reference reflection equivalence of all areas of the weld seam is obtained; 4) when a flaw echo is discovered during the detection process, the area of the reflector in the weld seam is determined firstly through a sound path and a probe K value, a corresponding reference equivalence is found out from the two-dimensional distance amplitude table to determine the reflection equivalence of the standard artificial reflector, and the equivalence of a flaw is obtained by comparing the reflection equivalence of the standard artificial reflector with the measured reflection strength of the flaw. Due to the adoption of the method, the technical problem of the accurate ration of the flaw of the austenitic stainless steel weld seam can be solved.