The landing site decision has direct relation to the safety of a spacecraft. This paper presents the use of computational geometry (CG) and genetic algorithm (GA) in the landing site selection. In order to describe the obstacles, we use computational geometry to compute the minimum enclosing circles and ellipses. Taking the obstacles as discrete circles and ellipses, we use the genetic algorithm to simplify and to solve the difficult problem of finding the largest empty circle (LEC) in circles and ellipses for the spacecraft landing on the surface. The results of tests on the solution procedure are presented.