The failure surface of elements can numerically represent by a concrete damage plasticity (CDP) model in Abaqus software which depends on five parameters. The parameters are eccentricity, shape, biaxial to uniaxial compressive strength ratio, dilation angle, and viscosity. This paper studies the effect of changing the values of the failure surface parameters on the bearing capacity, deflection, and overall structural behavior of ultra-high performance concrete (UHPC) beams. The parameters' changes include reasonable values higher or lower than the values adopted by Abaqus. An experimentally performed reinforced UHPC beam is simulated by Abaqus, and the five parameters are calibrated to coincide with the practical results. Then, one of the parameters is changed while others remain constant for each alteration to study its effect on the UHPC beam behavior. The numerical analysis results show that all five parameters do not affect the loading capacity and the corresponding deflection at the first cracking state. At peak state, the eccentricity does not affect the load and deflection. The influence of shape and the biaxial to uniaxial compressive strength ratio are confined to the deflection at peak load only without affecting the bearing capacity. The dilation angle effect appears when it is greater than 30 degrees to 56 degrees, while when it is less than 30, it does not affect the load and deflection. Rising the dilation angle and viscosity value promotes the peak load and the deflection.