In order to improve the therapeutic effect of breast cancer patients, trastuzumab combined with chemotherapy followed by radiotherapy was applied to breast cancer patients in this study and to observe the effect of this treatment on the abnormal rate of electrocardiogram and serum indexes of breast cancer patients. 60 patients received targeted therapy and chemotherapy during perioperative period. All patients received local radiotherapy after surgery. At the same time, for patients with poor peripheral blood vessels, jugular vein or subclavian vein catheterization should be performed before chemotherapy to avoid vein inflammation. The abnormal rate of electrocardiogram and serum indexes and rate of adverse reactions of 60 patients were examined. The results show that the abnormal electrocardiogram rate at T1, T2 and T3 was gradually increasing. The serum indexes after chemotherapy and radiotherapy are lower than those before chemotherapy and radiotherapy respectively. After chemotherapy and radiotherapy, there were 3 cases of radiation pneumonitis, 2 cases of pain and 2 cases of abnormal liver function. Postoperative chemotherapy and radiotherapy combined with trastuzumab can decrease serum levels in breast cancer patients. Meanwhile, the abnormal rate of electrocardiogram and cardiotoxicity were higher. Therefore, before trastuzumab therapy, cardiac function safety tests should be conducted in breast cancer patients and cardiac function should be closely monitored.