The invention discloses a flexible capsule for deep rock mass simulation test loading. A sealing channel embedded in the flexible capsule is made of a steel cylinder, the end, embedded in the flexible capsule, of the steel cylinder is sealed by a steel circular plate, the other end of the steel cylinder is open, and the steel circular plate is screwed into the sealed end of the steel cylinder from the open end of the steel cylinder through a thread on the inner wall of the steel cylinder till the outer surface of the steel circular plate is flush with the end face of the sealed end of the steel cylinder; two circles of annular bosses, namely the outer annular boss and the inner annular boss are further arranged on the outer side of the sealed end of the steel cylinder, the annular bosses are fixedly connected with the flexible capsule through vulcanization sealing, and the end face of the outer annular boss and the end face of the sealed end of the steel cylinder are flush with the side face of the flexible capsule. The sealing channel is prearranged in the flexible capsule through vulcanization fixed sealing, so that the problem of sealing of the flexible capsule at the position of an excavation opening is solved and uniform test specimen boundary loading is achieved.