Energy consumption and coverage problem are two important issues in wireless sensor networks. In this paper, we are going to maintain sensing coverage in a heterogeneous wireless sensor network with an adjustable sensing range that is randomly developed, in such a way that small numbers of sensor nodes are active, and therefore a small amount of energy is consumed, and the network lifetime increases. This is a multi-objective optimization problem. We used a Multi-Objective Evolutionary Algorithm based on Decomposition (MOEA/D) for solving this problem. The experimental results demonstrated that MOEA/D can perform better than NSGA-II.