According to Baidu map, Beijing West Railway Station to Tsinghua University Metro take Metro Line 9 → Metro Line 4 Daxing Line. The specific route is as follows:

Walk about 10 meter from Beijing West Railway Station, take Metro Line 9, pass four stops, reach the National Library, walk about 70 meters, take Metro Line 4 Daxing Line, pass six stops, reach Yuanmingyuan, walk about 620 meters, and reach the destination of Tsinghua University.