Objective: To observe the incidence of unreasonable use of high beam at nighttime among motor vehicle drivers, so as to provide the evidence for the prevention and control of road traffic injury. Methods: Four roads into city and five urban roads were selected in Yongkang of Zhejiang Province. An automatic recording system was used to collect the unreasonable use of high beam among motor vehicle drivers on the selected roads from 19:00 to 5:00 on Monday, Wednesday, Friday and Sunday during a week in July 2020. The regression tree model was used to analyze the relationship of the unreasonable use of high beam with road, time and traffic flow. Results: A total of 89 989 motor vehicles were observed, and 2 419 motor vehicle drivers had unreasonable use of high beam, with an incidence rate of 2.69%. The incidence rate of the unreasonable use of high beam was 3.14% in the roads into city, which was higher than 2.30% in the urban roads ( P<0.05 ). The incidence rates of the unreasonable use of high beam in the roads into city and in the urban roads were 5.15% and 2.90% on Wednesday, which were higher than those on Monday ( 2.89% and 2.34% ), Friday ( 2.90% and 1.92% ) and Sunday (2.06% and 2.12%). The highest incidence rate of the unreasonable use of high beam in the roads into city was 6.07% between 4:00 and 5:00, and in the urban roads was 4.50% between 2:00 and 3:00. The results of regression tree classification analysis showed that the highest incidence rate was 8.13% on the roads into city in the east, west and south directions, and on the urban roads in the east and north directions with less than 317 vehicles per hour on Wednesday. Conclusion It is more likely for motor vehicle drivers to use high beams unreasonably at nighttime on the roads into city with less traffic flow.