Ultrasonic　tomography　(UT)　is　a　nondestructive　technique　that　is　widely　applied　in　industrial　process　imaging.　In　this　paper,　a　novel　sector　diffusion　method　for　construction　of　a　sensitivity　matrix　is　proposed　to　improve　the　performance　of　a　linear　back-projection　(LBP)　algorithm.　The　so-called　sector-diffusion-matrix-　based　LBP　(SLBP)　was　applied　to　reconstruct　gas/liquid　two-phase　flow.　A　series　of　models　has　been　established　to　evaluate　the　effectiveness　of　the　method.　The　images　reconstructed　by　traditional　LBP　and　SLBP　are　presented　and　compared.　Two　quantitative　evaluation　criteria　including　position　error　and　image　correlation　coefficient　(I-cr)　were　defined　and　used　to　evaluate　the　quality　of　the　reconstructed　images.　The　imaging　results　indicate　that　the　SLBP　method　is　valid　and　feasible　to　improve　the　quality　of　reconstructed　images,　especially　for　a　UT　system　with　a　small　number　of　transducers.　The　evaluation　criterion　Icr　is　improved　by　26%,　20%,　9%,　and　4%　for　four　different　flow　patterns　with　an　eight-transducer　UT　system　in　128　x　128　pixels　and　improved　by　26%,　20%,　10%,　and　1%　in　40　x　40　resolution.