To sort different sizes of apples, a kind of passive grab cable-driven of flexible manipulator is designed. Each finger consists two single degree-of-freedom joints and a torsional spring is installed on each joint. The two-point of finger is stretched by a cable, which is connected to pistonstem of cy- linder. However, when the cable looses,the torsional spring drive the finger bend and grab the apple. The objective function is determined by the minimum change range of grasping force, Which can be optimized by the fmincon-function provided by the software MATLAB. We can conclude that: twist the stiffness of hydropneumatic spring are k2 and k3 ,preloaded angle are Φ02 and Φ03, moreover it show that the manipulator has a good supple adaptation without causing damage to apple.