The number exceeded the record of 12.679 million set the previous day, according to China Railway Corporation (CRC).
Railway passenger traffic for Monday was expected to fall to 10.68 million trips, and 957 more train services were added.
The Spring Festival travel period, also known as the Chunyun, lasts for 40 days from Feb. 1 to March 12 this year.
Although the travel period is coming to an end, passenger traffic may stay high in the coming days as many migrant workers started to return to where they work after the Lantern Festival which fell on March 2.
In Nanchang, east China's Jiangxi Province, for instance, additional train services have been provided to cope with the passenger flow into big cities such as Guangzhou, Shenzhen and Shanghai.