This study investigates the blast effect on hoop stresses and displacements created on the wall of over-ground reinforced concrete water tanks and the effects of blast waves, and the water structure interaction using ABAQUS software. Therefore, the main goal of this research is to investigate the behavior of the above-ground tanks under the effect of blast loads, taking into account the geometric characteristics, power of blast and the distance between the explosive materials and the tank. For this purpose, the main variables in the current research include the geometrical shape of the cross section of the concrete tank (circle and square with equivalent area), the amount of explosive materials (500 and 1000kg) and the distance of explosive materials from the tank (10 and 25 meters). Also, the responses studied include maximum von Mises stress, maximum displacement created in the tank, kinetic energy and failure index. The obtained results show that by changing the cross section of the tank from circular to square, the responses of maximum von Mises stress has been increased by 9.1%, maximum displacement has been increased by 35.9%, kinetic energy has been decreased by 6.43% and failure index has been increased by 3.7% respectively. Also the results show that by increase of the explosive substance, the responses of maximum stress, maximum displacement, kinetic energy and failure index have been increased by 33%, 44.4%, 6.55% and 13.3% respectively. Other results show that by a 15-meter decrease in the distance of the explosive material from the tank, the responses of maximum stress, maximum displacement, kinetic energy and failure index have been increased by 42.2%, 9.9%, 8.16% and 8.23% respectively.