This creation is a bag structure of a bicycle is connected to seat pipe under seat of a bicycle, wherein the bag structure contains a bag body, a capacity bag and a lifting belt, wherein bicycle body extends a connecting part capable of buckling the seat pipe. The capacity bag can be contained in body of the bicycle bag and the bicycle bag is composed of a first sheet body and a second sheet body, thus the bicycle bag can place the capacity bag in the bicycle body and make it spread out when opening and make opening between the first sheet body and the second sheet body penetrate the seat. Edge of the first sheet body and the second sheet body is provided with a seal structure, which is used for sealing any three continuous edges of the first sheet body and the second sheet body to form a capacity space, to make bicycle capable of being placed in the capacity space, more convenient for people to take.