In order to solve the problems that the force signal of the slave is always mixed by large noise and the higher price of the force sensor, position-velocity type of force feedback algorithm is set up based on position feedback in the original bilateral hydraulic servo control system with force feedback in which the force feedback rod served by hydraulic is used as the master side. Least square is used for system identification and build force feedback model of slave free motion, according to the displacement differential between the master and slave to detect the slave's contacting with environment. Experiments on the bilateral hydraulic servo control system with isomorphism master and slave verified the validity of the algorithm and it can be widely used to various hydraulic systems with force feedback control.