The invention discloses a sealing device of a rock sample in a true triaxial test, which comprises bearing cushion blocks, sealing rubber bars, silica gel coating, a rock sample and antifriction gaskets, wherein the four bearing cushion blocks are respectively sequentially arranged on four end parts of the rock sample, which are performed rigid load in two directions, and one end of each bearing cushion block is in alignment with the rock sample in a mutually buckled way; the bearing cushion blocks and the end parts of the rock sample are provided with the antifriction gaskets, each antifriction gasket consist of a polyfluortetraethylene sheet, a red copper sheet and solid antifriction material such as graphite or zirconia, and the like, one side of the red copper sheet is stuck to the end part of the rock sample; and the rest two end parts of the rock sample, which are to be performed flexible load are coated with organic silicon gel and are covered by the bearing cushion blocks, anda sealed integer is formed by the rock sample dried in a oven and the bearing cushion blocks. The sealing device has simple structure and simple and convenient operation, is adapted to the two-rigidity one-flexibility load method of the mogi type and true triaxial type and solves the problem of stress concentration of the rock sample caused by blank corners.