Abstract: A numerical simulation of the wing diffuser was conducted to optimize the performance of the centrifugal compressor of a marine engine turbocharger. The diffuser blade was treated with low-solidity and the blade root was slotted in order to study the influence of both low-solidity and slotting treatment on the performance of the whole compressor. The results indicate that low-solidity treatment can widen the flow range at all speed,but the stall boundary is also shifted to the right. Combining low-solidity and slotting treatment can keep the choked flow rate constant,increase stall margin at full speed,and solve the migration problem of stall boundary under the condition of broadening the flow range. It can achieve stable flow at twice higher speed than the vaneless diffuser. Although combined treatments can reduce aerodynamic performance,its performance still is higher than that of the vaneless diffuser. The radial location of slot is a key parameter in the slotting treatment. It not only affects the flow range,but also causes a fluctuation of nearly 4.0% in the peak efficiency and a fluctuation of nearly 1.5% in the peak pressure ratio. Therefore,it needs to be preferentially determined.