This study aims to analyze the productivity of the NN pattern and reveal the formation mechanism of French compound nouns. The NN pattern could embed complex structure on N1 or N2 and the constitutive elements are linked in a hierarchical relation. The analysis is conducted from four levels: structure hierarchy, compounding method combination, semantic relation and semantic class combination. A pattern should be defined by four parameters and their productivities for forming compound nouns vary with vocabulary. The formation process is analyzed based on the corpora, which are elaborated by annotating both the formal and semantic information. This study presents in detail the formation mechanism of NN compound nouns and it allows well predicting the production of compound nouns. The analysis method could be applied to other patterns and vocabularies. The annotated resource and analysis results contribute to the research in language acquisition, lexicography and natural language processing.