Abstract: Lamb wave scattering near a lap fillet weld was studied in a prospect to inspect the pipeline section under a B-type sleeve. An analytical model based on mode matching technique was developed and used for scattering-coefficients evaluation in a given frequency range. The results were verified by those obtained from time-domain finite element simulation and frequency and wave number analysis using two-dimensional Fourier transform. It showed that through the fillet weld, about 80% energy flux of a0 mode, or at most about 37%-89% of s0 mode might get into the sleeve-covered pipeline without mode conversion at 2 200-2 600 kHz ·mm or somewhere smaller than 1 600 kHz ·mm corresponding to the weld shape or sleeve thickness. The research may provide an entry for the sleeve-covered girth weld investigation.