To systematically evaluate the effects of modifed Gancao Xiexin Decoction on oral ulcer after radiotherapy and chemotherapy.Methods:A comprehensive search of 8 Chinese and English databases such as the National Knowledge Infrastructure Database(CNKI)and PubMed，and the collection of randomized controlled trials academic papers on the treatment of oral ulcers after radiotherapy and chemotherapy with Gancao Xiexin Decoction，from the establishment of the database to September 2020 were retrieved.476 papers were initially retrieved.After excluding duplicates and documents that did not meet the inclusion criteria，8 RCTs were finally included，including 553 patients，279 cases in the test group，and 274 cases in the control group.2 reviewers were selected for screening and selection.After literature selection，data extraction，and evaluation of the risk of bias，RevMan 5.3 was used to conduct a meta-analysis of the research data.Results:The total effective rate of modifed Gancao Xiexin Decoction in the treatment of radiation and chemotherapy in patients with oral ulcers（RR 1.29，95％CI 1.19 to 1.40，P<0.000 01); Healing time（MD-3.16，95％CI-4.65 to -1.67，P<0.000 1），the pain relief rate on the 5th day(RR 1.72，95％CI 1.32 to 2.24，P<0.000 1); the pain relief rate on the 7th day(RR 1.41，95%CI 1.20 to 1.66，P<0.000 1)，there was significant difference between the 2 groups; Subgroup analysis indicates：Compared with normal saline group，Ganxiexin Decoction was more effective in treating oral ulcers after radiotherapy and chemotherapy(R 1.29，95%CI 1.16 to 1.43，P<0.000 1).Conclusion:According to the existing literature，Gancao Xiexin Decoction is an effective prescription for the treatment of oral ulcers after radiotherapy and chemotherapy.But limited to the quality and quantity of the included studies，the verification of the results of this study requires higher quality and larger samples in future studies.