In this study, we used bioinformatics approaches to retrieve 11 family genes encoding for PAO from tomato genome, which were further named as SlPAO111 grouped into three subfamilies (Ⅰ, Ⅱ, and Ⅲ). In addition, gene structure analysis, protein secondary structure prediction and subcellular location prediction results are demonstrated that SlPAOs gene family have distinct subfamily categorization characteristics. Sequence and phylogenetic analysis suggest that SlPAO18 belonging to subfamily Ⅰ and Ⅱ are typical PAO genes. Proteins encoded by SlPAO911 belonging to subfamily Ⅲ contain specific SWIRM domain, SlPAO911 are characterized as histone lysinespecific demethylases, but not real PAO. Then, we used qRTPCR to analyze the relative expression level of 8 typical SlPAOs (SlPAO18) in different tissues (dry seeds, fresh leaf, cotyledon, stem, root) of tomato plant, the results showed that the expression levels of SlPAO18 in different tissues were significantly different. It is speculated that there may be a certain correlation between the diversity of expression and functional diversity of the SlPAOs gene family.