The ninth week (April 18-24) of the school calendar in Tsinghua University is the anniversary week, and April 24th is the anniversary day. Activities are mostly concentrated on 23rd and 24th (showing that a large number of alumni have returned to school, and cultural performances have increased greatly).

Broadly speaking, it starts from April 18 and ends on the 24th. In a narrow sense, it starts on the morning of 23rd and ends at midnight on 24th. 25th is the first day of the new century.