Objective To explore he value of M-mode ultrasound combined with atrioventricular ladder diagram in the diagnosis of fetal arrhythmia. Methods The activity curves of the atrioventricular wall, atrioventricular valve and semilunar valve were obtained in fetal echocardiography with M-type ultrasound sampling line, and the types of fetal arrhythmias diagnosed by atrioventricular trapezoid map were retrospectively analyzed in Chongqing Healthcenter for Women and Children from January 2016 to October 2020. Results A total of 165 cases of fetal arrhythmia were diagnosed by M-mode ultrasound combined with atrioventricular ladder diagram, including 76 cases of atrial premature contractions (46.1%), 6 cases of ventricular premature contractions (3.6%), and 43 cases of sinus tachycardia (26.0%) , 8 cases of supraventricular tachycardia (4.8%), including 1 case of atrial tachycardia (0.6%), 1 case of atrial flutter (0.6%), 22 cases of sinus bradycardia (13.3%), atrial Ventricular block was found in 9 cases (5.5%). Conclusion M-mode ultrasound combined ith atrioventricular ladder diagram is feasible to diagnose fetal arrhythmia. This method is simple and intuitive, and can identify the type of fetal arrhythmia.