Wood-plastic structural planks made of polyethylene (PE) and poplar flour were used as a packaging material of ammunition. Reliability analysis of the planks is of great significance for safety in service. The modulus of elasticity and static bending strength of the planks were obtained by experiments. The first and second order moment method (FOSM) was used to analyze the reliability of the structural planks. The result showed that the wood-plastic structural planks with higher density have a better reliability than that with lower density. The purpose of this research was to provide reference for wide application of wood-plastic structural planks.