Abstract: In conventional haptic feedback technologies,impedance control is used as the main control mode,which can hardly meet the requirements in virtual assembly.Admittance control mode is more suitable for haptic rendering.The framework and algorithms of the haptic rendering based on admittance control mode are presented.First,dynamics model used for admittance control is given,and haptic rendering under the states of collision and constraint are discussed.Second,to solve the problem of small clearance assembly,a method of haptic rendering combining physical constraints with geometric constraint is presented.Third,the method of quadratic Lagrangian interpolation is adopted,aiming at solving the problem of asynchrony between haptic feedback loop and physical computing loop to maintain the stability of the haptic device.The algorithms are implemented and the haptic device is connected and utilized in the virtual assembly process planning system(VAPP).The results show that the algorithms can meet the need of haptic interaction in the virtual assembly system.