This paper studies the numerical analysis of a three dimensional incompressible laminar fluid flow on rectangular fins with circular perforations which stands on a flat surface. Perforations by circle cross sections are scattered on the length of the fin and the number of holes is variable between 1 to 2. The Simple algorithm is the main approach to solve the problem. To the end of discretization of momentum and energy equations, the second order upwind technique has been employed. The Reynolds number is assumed between 100 to 350 concerned to the thickness of the fin. The main contribution of this paper is finding the optimum place of perforations and afterwards compare the thermal performance and Nusselt number of the fins with one and two perforation and solid fin. The results showed the fin with two perforation has the higher thermal performance than both the fin with one perforation and solid fin. The main novelty of this paper is in using circular perforation, as expected, due to the lower weight of fin with two perforation than other mentioned fins it has bigger heat transfer coefficient compared to both others. The advantages of circular perforation can be mention as economical reasons and simpleness of implementation as compared to other developed techniques in the literature.