Since UML activity diagrams are essential tools for software requirements analysis, automating the process of generating UML activity diagrams helps reduce development time and labor costs. Existing approaches directly extract the elements and their relations of a UML activity diagram from unstructured natural language requirements either by manually constructing extraction rules or adopting data-driven approaches. However, these approaches typically consider only the syntactic features of software requirements statements while neglecting the semantic features. This leads to potential errors or redundancies in the automatically generated UML activity diagrams. Therefore, this study proposes an automated approach for constructing activity diagrams that combines the semantic features of software requirements statements in Chinese. This approach integrates the relevance between software requirements statements and UML activity diagrams, as well as the temporal properties of the software requirements statements, to extract UML activity diagram elements and their relations. It compensates for the shortcomings of existing approaches, which are easily disrupted by irrelevant information in the requirements and struggle to correctly represent various business activities. Experimental results on 100 industrial cases validate the superiority of the proposed approach over state-of-the-art approaches in terms of the completeness, correctness, and redundancy of automatically generated UML activity diagrams.