A new type of flexible pneumatic bending joint (FPBJ) and its mathematical model were proposed. To implement its real-time closed-loop control system, its mathematical model was simplified, and the mechanical characteristics were studied experimentally. An experimental platform for mechanical characteristics testing was set up, and two FPBJs with different length(40mm and 60mm) were tested. The experimental results were analyzed with Matlab curve and surface fitting toolbox, and the FPBJ empirical model was derived. The model showed a non-linear relationship among the bending angle, the FPBJs internal and external pressure difference, joint length and the output force of the FPBJs. Contrast to the simplified mathematical model, the empirical model was more precise, the mean relative error of output angle model was less than 6.7%, and the mean relative error of output force model was less than 2%. Meanwhile, an error, the joint length is proportional to the bending angle in the mathematical model, was avoided in the empirical model.