The internet has brought great changes to college students' lives. The most typical phenomenon is more and more students are staying up late, especially freshmen. This paper intends to understand the habit of staying up late in university freshmen and analyze the main influencing factors so as to improve university freshmen's healthy sleep habits in the network era. The method used was the self-made questionnaire to investigate university freshmen in universities in Hangzhou by anonymous survey. The results showed that only 2% of freshmen never stay up late, 53% of freshmen stay up late sometimes, and 45% of freshmen always stay up late. Almost 68% of freshmen go to bed between 12:00 pm to 1:00 am. During their vacation, 30% of freshmen go to bed after 1:00 am. The results also show that 78% of freshmen who stay up late spent their time on the internet. Staying up late is becoming a common phenomenon among university freshmen in the network era. The main reasons include the popularity of mobile phones, the convenience of the internet, online social networking, a lack of self-control, and so on. Society, university and freshmen should pay more attention to this and put efforts together to develop healthy sleep habits.