This article investigates the influence of conceptual flow simulation model parameters (i.e coefficients and constants that need to be estimated in calibration) on model solution (surface runoff) to understand the characteristics of the model. A new conceptual watershed yield model (WYM) was employed. There are four physical parameters, two fitting coefficients and two initial estimates of the surface water and groundwater storages that control the functioning of the model. The conceptual model was applied on Ling River near Kahuta and detailed sensitivity analysis was performed to explore the most sensitive model parameters. The most sensitive model parameters worked out were Cg (a fitting coefficient, which reflects the rate at which groundwater runoff occurs), wr (watershed retention is the initial rainfall losses before runoff begins), pgr (input parameter that reflects the discharge capacity of the groundwater aquifer). The model parameters like ic (infiltration coefficient), gwsm (input parameter that depends on the subsurface storage available in the watershed) and ep (input parameter) have negligible effect on model solution. It was observed that wr (watershed retention) is the only surface runoff controlling parameter and pgr and Cg are the groundwater runoff controlling parameters.