FGW are expecting it to be very busy and are asking people to buy tickets in advance.
Phil West, First Great Western's Special Events Manager says: "We are expecting huge demand for our train services. That's why we recommend that Cardiff City fans buy their train tickets as soon as possible if they want to be sure of travelling by train."
Three extra trains containing 10 coaches (larger than standard services) will be added to the outgoing schedule on Sunday morning and then three extra trains coming home after the game.
A queing system will be put in place at both stations.