The lube oil and cooling water channel were designed for a new developed medium-speed diesel engine, which resulted in big difficulty in machining. Combined cutting tool, high-speed alloy milling cutter and parabola depth drill were applied as well as some advanced machining technology, which can satisfy the machining requirements of cylinder block and enhance efficiency, and avoid bad influence of machining stress on the key parts of cylinder block. High-precision measuring tool and optical instruments were employed instead of 3D measuring to accomplish the measuring of key dimensions and points of cylinder block.