Objective To investigate the effect of rapid maxillary expansion combined with straight wire appliance on periodontal indicators in patients with maxillary constriction with malalignment. Methods A total of 120 patients with maxillary constriction with malalignment admitted to People's Hospital of Yilong County from December 2023 to December 2025 were selected, and they were divided into the control group and the study group by the random number table method, with 60 patients in each group. The control group was treated with straight wire appliance, and the study group received rapid maxillary expansion combined with straight wire appliance. The periodontal indicators, dental arch changes, cephalometric measurements and complication rate were compared between the two groups. Results After treatment, the scores of PLI, GI and SBI in the study group were lower than those in the control group (P<0.05). After treatment, the maxillary length of the study group was shorter than that of the control group, and the maxillary width was larger than that of the control group (P<0.05). After treatment, the MP-SN and U1-SN angles of the study group were smaller than those of the control group (P<0.05). There was no statistically signiffcant difference in the incidence of complications between the two groups (P>0.05). Conclusion For patients with maxillary constriction with malalignment, combined treatment with rapid maxillary expansion and straight wire appliance can effectively improve periodontal indicators, and exert positive effects on reshaping dental arch and craniofacial structure, with good safety.