The assembly process is one of the most important spots in the process of product production. the assembly workload accounts for 20% to 60% of the manufacturing workload for mechanical products. A suitable assembly sequence can not only reduce the assembly workload, but also reduce the manufacturing cost of products. Therefore, this paper proposes a product assembly sequence planning method based on semantic process knowledge. Firstly, a research framework of product assembly sequence planning based on semantic process knowledge was constructed by analyzing the requirement of product assembly sequence planning for assembly process semantic knowledge. Secondly, an assembly semantic process knowledge information model was proposed, which included hierarchical structure information, attribute information and semantic information of sub-assembly. Based on this, assembly sequence planning ontology and SWRL (Semantic Web Rule Language) assembly semantic rules were constructed in Protege software. Thirdly, based on the analysis of product model structure and assembly sequence planning process in a drive axle of construction machinery, sequence traversal algorithm was established for traversing sub-assembly structure. Aiming at the structure of atypical sub-assembly group, an iterative modification method for inferring the sequence of atypical sub-assembly group was designed. Finally, Taking the assembly sequence planning process of drive axle of construction machinery as an example, the construction method of assembly semantic process knowledge information model and the assembly sequence planning decision technology in this thesis were applied to verify the reliability of the information model.