Abstract: 【Objective】The aim was to analyze the differences in transcriptome， physio-biochemical and cytological levels of avocado mesocarp with different oil contents， so as to provide reference basis for mining related genes in fatty acid synthesis process of avocado mesocarp and breeding new varieties of avocado. 【Method】The mature mesocarp of three avocado varieties Hass， RL-1 and RL-2 were used as experimental materials， and the Illumina HiSeq 2500 sequencing platform was used to complete the sequencing. With |log₂ Fold Change|>1 and P<0.05 as the standard， the differentially expressed unigenes were obtained by DEGseq（v2）. The differentially expressed unigenes in the three comparison groups （RL-1 vs Hass， RL-2 vs Hass and RL-2 vs RL-1） were analyzed by Venn diagram and volcano diagram. Through GO functional annotation， KEGG signaling pathway enrichment and cluster analysis， real-time fluorescence quantitative PCR was used to verify the transcriptome sequencing results， and the oil contents of three avocado varieties were determined. The oil body in the mature mesocarp of avocado was observed under a 40-time objective lens by laser confocal technique. 【Result】Among transcripts of three varieties of mature avocado mesocarps， a total of 19007 unigenes were found to be significantly different between at least 2 transcripts of samples （P<0.05， the same below ）. There were 3000 unigenes with obvious differences in relative expression among three comparison groups. In the RL-2 vs Hass comparison group， there were 9 functional items and they were significantly enriched. In the RL-1 vs Hass comparison group， only 3 functional items under the cell component category were significantly enriched. Only two KEGG signaling pathways were significantly enriched in the RL-2 vs Hass comparison group. A total of 32 differentially expressed unigenes involved in fatty acid synthesis in avocado mesocarp were screened. The results of cluster analysis showed that the expression patterns of differentially expressed unigenes were divided into two groups. The results of real-time fluorescence quantitative PCR showed that the transcriptome sequencing data were reliable. The oil contents of the mature mesocarp of the three avocados varieties were ranked as Hass>RL-2>RL-1. The observation results of the oil body difference of the avocado mesocarp showed that the mature mesocarp of Hass had larger oil bodies， and the maximum diameter was 15-20 μm. 【Conclusion】 A total of 32 differentially expressed unigenes related to the synthesis of fatty acid components in avocado mesocarp are screened， among which five unigenes ［PaPDH （E1β）， PaACP4-1， PaACP4-2， PaSAD（FAB2） and PaFaTA］ had higher relative expression levels in mature mesocarp of three avocado varieties.