Abstract: Objective By observing the changes of time domain parameters of heart rate variability (HRV) in patients with generalized anxiety disorder (GAD), we tried to find a reliable physiological quantitative index. Methods From June 2017 to October 2019, suspicious GAD patients in Jiangsu Province Hospital of Chinese Medicine were selected. Beck Anxiety Inventory (BAI) was used to select 56 GAD patients with BAI score≥45 as observation group and 52 healthy people with BAI score <45 were recruited as control group. Ambulatory electrocardiogram (AECG) was performed in both groups and 5 HRV time domain parameters were measured and compared. The function of parasympathetic nerve was reflected by the percentage of the number of heart beats whose R-R interval difference is more than 50 ms to the total number of heart beats (pNN50) and the root mean square of the difference between adjacent R-R intervals (rMSSD). The mean value of standard deviation of R-R interval every 5 min (SDNN index) reflected the change of sympathetic tension .The standard deviation of all R-R interval (SDNN) reflected the whole regulation ability of autonomic nerve. The ratio of the total R-R interval to the maximum R-R interval frequency (trigonometric index) expressed all HRV within 24 h. Results Compared with the control group, pNN50,rMSSD and SDNN-Index in the observation group were significantly decreased (P＜0.05), but there was no significant difference in SDNN and trigonometric index between the two groups (P＞0.05). Conclusions GAD patients are characterized as decreased parasympathetic function and increased sympathetic activity.