Objective To establish a mouse model of endometriosis with fibrosis and to study its application. Methods A mouse model of endometriosis with fibrosis was established by modified intraperitoneal injection using BALB/ c mice; the peritoneal lavage fluid of mice was collected and the level of TGF-β1 in lavage fluid was detected by ELISA. The degree of abdominal adhesion was scored and the success of the endometriosis model was verified by hematoxylin-eosin(HE)staining, while the collagen deposition in the ectopic focus was detected by Masson staining and the degree of collagen deposition was evaluated. The expression of fibrosis-related proteins E-cadherin, collagen I, α-SMA, and smooth muscle myosin heavy chain II ( SMMHC-II) were detected by immunohistochemistry, and the degree of ectopic fibrosis was evaluated. Results The success rate of a mouse model of endometriosis with fibrosis constructed by a modified intraperitoneal injection method could reach 100%. The level of TGF-β1 in the peritoneal lavage fluid of mice increased significantly with the extension of modeling time. Masson staining and immunohistochemical staining of fibrosis-related proteins revealed a fibrotic phenotype in the abdominal cavity of endometriosis mice. Conclusions The improved intraperitoneal injection method has a high success rate in the establishment of a mouse model of endometriosis with fibrosis. TGF-β1 levels in peritoneal lavage fluid, Masson staining, and immunohistochemical staining of fibrosis-related proteins can evaluate the degree of pelvic fibrosis in mice with endometriosis.