Objective:To explore the effect of the method "four-step posture gargle" on the prevention of oral mucositis (OM) in patients with blood tumor after chemotherapy.Methods:A total of 90 cases with malignant hematological diseases who were treated with chemotherapy in the department of hematologic oncology from January 2018 to June 2019 were selected by convenient sampling method. The control group used "drum gargle", and the test group used "four-step posture gargle". Oral evaluation was conducted on the days of using chemotherapy day, 3d, 7d, 14d and 21d after chemotherapy. The differences of OM occurrence days, OM grading, OM healing time, oral pH value and chemotherapy delay days were compared between the two groups.Results:No significant difference was found between the two groups in OM days and the number of patients with delayed chemotherapy ( P >0.05). After chemotherapy, the oral pH value of the test group was 6.53±0.64, higher than that of the control group (6.01±0.57). The healing time of OM in the test group was (6.76±1.82) d, shorter than that of the control group (8.87±3.06) d, which were with statistically differences ( t value was 4.047 and 3.978, P <0.05). Group level 0, Ⅰ, Ⅱ, Ⅲ, Ⅳ OM cases respectively, 6, 8, 8, 17, 6 cases were lower than the control group of 10, 11, 12, 10, 2 cases, with statistically significant differences ( χ 2 value was 8.000-27.000, P < 0.05). Conclusions:"Four-step body position gargle method" provides a new method of oral care for patients with hematological tumor. The method can effectively reduce the occurrence of oral mucositis, reducing disease-related complications, improving treatment continuity.