These three places are relatively close, all in Haidian District. You go to Peking University first. If Peking University doesn't accept tickets, you can enter from the west gate and exit from the east gate. After that, you can sit in Tsinghua West Gate instead of going to Tsinghua Campus.

Scheme 1 through train

Tsinghua University Ximen takes bus No.319, gets off at the south gate of Yuanmingyuan, and walks to Yuanmingyuan.

Scheme 2 through train

Tsinghua University Ximen takes bus No.320, gets off at the south gate of Yuanmingyuan, and walks to Yuanmingyuan.

Scheme 3 through train

Tsinghua University Ximen takes bus No.331and gets off at the south gate of Yuanmingyuan and walks to Yuanmingyuan.

Tickets for Yuanmingyuan are now in 30 yuan.

Then go to the botanical garden:

Scheme 1 through train

Walk to the south gate of Yuanmingyuan, take bus No.331and get off at the south gate of Beijing Botanical Garden.

Scheme 1: turn 1 time.

Step 1: Walk to the south gate of Yuanmingyuan, take bus No.319 and get off at Xiyuan.

Step 2: Take bus No.634 in Xiyuan and get off at the south gate of Beijing Botanical Garden.

The entrance ticket to the Botanical Garden is 5 yuan.