Here we consider the effect of gravitational lensing on the power spectrum of the Cosmic Microwave Background. In this way gravitational lenses and the CMB power spectrum are explained and their equations are discussed. Gravitational lenses are usually the massive objects on the way of the light through the space toward us and causes the deviation of the light from its original path. It is because of the additional curvature that causes by the object. In the other hand the CMB power spectrum is defined by the temperature difference between two space position. So the deviation of the light path which will be the reason for changing the temperature distribution, will affect the CMB power spectrum. This effect is considered by assuming a additional potential in the equations. This potential will give us the angular separation at the presence of the lens, comparing to the situation without the lens. The gradient of this additional potential can determine the effective convergence by the lens, which is a function of ?. One can see that the correlation function of the effective convergence will be handed by calculating the correlation function between the point in the angular position ? and ?+?. It is possible to use this method for shear correlation function. So we have the power spectrum of the effective convergence and shear. These are almost enough to calculate the effect of gravitational lensing on the CMB power spectrum. The result of computing this effect shows that because of the lens, a coefficient will appear on the CMB power spectrum equation. This coefficient is a function of the angular separation and has gaussian distribution. This coefficient will smooth the CMB power spectrum.