In order to solve the problems of signal mixing and inaccurate detection in residual stress detection of welded joints due to complex weld structure， this paper proposes an ultrasonic non-destructive testing method for residual stress of welded joints based on intrinsic mode function （IMF） and improved empirical mode decomposition （EMD）. This method loads non-stationary EMD components of the heat source and extracts the distribution characteristics of heat flux density； generate autocorrelation functions and power spectral density features through time function operations to suppress modal interference； decompose the signal using the improved EMD algorithm of IMF and calibrate the stress acoustic elasticity coefficient； combining acoustic elastic effect to detect residual stress. The experimental results show that the longitudinal stress is stable in the middle section of the welded joint， with an average of 160 MPa and an edge of -95 MPa. The transverse stress is -57 MPa in the middle section and 125 MPa at the edge. The detection results of this method have a similarity ROC curve area of 0.95， significantly higher than the comparison methods. From the above data， it can be concluded that this method achieves high-precision non-destructive testing of residual stresses in welded joints by accurately separating stress sensitive frequency bands， which can provide reliable basis for welding quality control.