The utility model discloses a flexible fixture based on magnetorheological fluid, which comprises a shell and clamping arms, and the clamping arms are uniformly distributed around the shell for a circle; a guide channel is formed in the side wall of the shell, and the clamping arms are installed in the guide channel. The clamping arm comprises a box body with one side open, a thermal expansion ring is arranged in the box body, and a magnet exciting coil is arranged between the thermal expansion ring and the box body. A sealing plate is arranged on the open side of the box body, and magnetorheological fluid is filled among the box body, the sealing plate and the thermal expansion ring; a plurality of ejector rods are further arranged in the box body, and one end of each ejector rod penetrates through the sealing plate; a baffle is arranged at the outer end of the guide channel, and at least one through hole is formed in the baffle. The clamp is convenient to use and better in clamping and positioning effect, workpieces of different shapes can be clamped through the clamp, adaptability is higher, machining of all faces of the same workpiece can be achieved only through one set of clamp, and therefore machining cost is greatly reduced.