<p>The enhanced adhesion between gastric cancer (GC) cells and peritoneal mesothelial cells (PMCs) is one of the key factors in the formation of the pre-peritoneal-metastasis adaptive microenvironment. USP35 belongs to the ubiquitin-specific protease family and is involved in regulating the occurrence and progression of various diseases. However, whether this gene can regulate the adhesion of GC cells to PMCs has not been clarified. The aim of this study was to identify the mechanism by which USP35 promotes the formation of the pre-peritoneal-metastasis adaptive microenvironment of GC and to find potential therapeutic targets. For the first time, we found that USP35 expression is upregulated in GC tissues, especially in peritoneal metastatic nodules, and is associated with poor prognosis. USP35 expression is the highest in MKN-45P, which is closely related to its high peritoneal metastasis potential. The mechanism of action involves several key steps. Firstly, the gene targets STING through de-ubiquitination and stabilizes its expression. Through this interaction, USP35/STING activates the HIF-1α/FAK pathway, promoting energy metabolism reprogramming and further improving the adhesion ability of GC cells. Secondly, exosome USP35 derived from GC cells has been shown to promote the mesothelial–mesenchymal transformation (MMT) of PMCs, preparing the “soil” for cancer cell adhesion and growth and contributing to the establishment of a pre-peritoneal-metastasis adaptive microenvironment. In summary, USP35 synergistically promotes the establishment of this environment through the dual mechanisms of regulating energy metabolic reprogramming of tumor cells and inducing the MMT of PMCs via the exosome pathway, providing a new theoretical basis for searching for therapeutic targets of gastric cancer with peritoneal dissemination.</p>