The soft manipulator has its unique advantages in picking some fragile objects，which has been the focus of research field of robot. In order to evaluate the overall performance of the soft manipulator and further realize the precise grasping control of manipulator, it is necessary to carry out modeling analysis and experimental research on the soft manipulator. A four-finger soft manipulator integrated with flexible strain sensor that can illustrate the bending angle of soft actuator was developed. Moreover, the mathematical model for predicting the bending angle and end output force of the soft actuator upon various pressure was established, and the influence of variable stiffness for constraint layer on output performance of soft manipulator was analyzed as well. Furthermore, hardware control system of soft manipulator was developed and experimented on the bending angle, and output force of the soft pneumatic actuator were performed. Experimental results showed that the force output of soft manipulator can be improved by changing the stuffiness of constraint layer. In addition, the experimental data agreed well with the theoretical analysis results, which validated the correctness of the proposed mathematical model. Grasping tests on several commonly fruits of various shapes and length such as strawberry, orange, pear and apple demonstrated that the soft manipulator can achieve nondestructive grasping of fragile and fragile objects easily. The envelope grasping force of the soft manipulator was up to 11.89N, and the fingertip grasping force was 2.81N. The research results can provide theoretical guidance and reference for the widely application of soft manipulator.