This paper brings forward a flexible fixture system based on magneto-rheological fluid. It is a holding and positioning device that has flexible surface of change rigidity by using current and magneto-rheological fluid valve to control variety of rigidity. It can adapt all kinds of rigidity and shape holding objects, the stress is adapted to object surface of any shape. Flexible fixture based on magneto-rheological fluid has simple structure and faster execution action and lower cost relative to pure mechanical control system. The simulation results are shown that the fixture system has better positioning precision and clamping effect. The fixture device can be applied in many domains.