Abstract: In this paper，we proposed a method of residual stress measurement for welded structure using Critically Refracted Longitudinal ( LCR) wave based on acoustic elastic theory．Acoustic time can reflect the residual stress existing on the surface and interior of the components，the key techniques of residual stress detection by LCR wave can be demonstrated.These techniques include LCR wave incitation，receiving and signal processing．The residual stress measurement system is designed and implemented in this paper．Acoustic time is a key value for the measurement system，the precision of the residual stress measurement depends on the key value．System implementation adopts the mode of“one sending and one receiving”，the residual stress is analyzed and evaluated through measuring the change of acoustic time on fixed-length．