Wireless sensor networks (WSNs) are a consolidated technology with high potential in the Internet of Things. One of the main challenges of WSN is energy optimization. Many routing algorithms have been proposed for saving WSN energy; however these approaches provide mono-objective optimization which is not suitable for most network performance conditions. In this regard, MOR4WSN is a WSN routing mechanism based on a multi-objective evolutionary optimization algorithm called NSGA-II. MOR4WSN aims to reduce network energy consumption through optimization of sensor distribution. This paper presents the crossover operator in MOR4WSN for energy optimization in hierarchical WSN based on NSGA-II.