Wind lens is the collection-acceleration device which shrouds a wind turbine. For given turbine diameter, the power augmentation can be achieved by Shroud diffuser, popularly known as wind lens. In this paper, a comparative numerical prediction of mass flow rates in the wind turbine has been carried out with various types of wind lens like straight diffuser with a brim, curved diffuser with the brim, stepped diffuser with the brim, bumped diffuser with the brim. All these eight diffusers are firstly analyzed in Ansys Fluent R14.5 for its velocity variation and pressure variation at inlet and outlet of the diffuser. From the CFD result From above CFD analysis, it is concluded that stepped diffuser with brim shows the higher percentage increase in velocity i.e. 80.33 %, as compared to bare wind turbine so stepped diffuser gave the good performance.