Separate heat source profile basing on structure of semiconductor laser array is applied in thermal resistance calculation of microchannel heatsink as boundary condition. Relationships between emitter width，position and thermal resistance are presented and optimized length of microchannel at different semiconductor laser arrays′ cavity length are also gotten through numerical calculation .Semiconductor laser array, with 1mm cavity length, 100 μm emitter width and 25% fill-factors is packaged on the presented microchannel heatsink and tested. With an exterior size of 27 mm×11 mm×1.5 mm，thermal resistance of microchannel heatsink reaches 0.34 K/W and matches the need of high power semiconductor laser array′s cooling.