The flexibility and adaptability of soft legged robots offer great promise for their application in complex environments. This paper presents the design of a modular pneumatic-driven soft tripod robot (MPSTR), where the soft mechanical legs consist of two bending modules with S-shaped curvature structures. Each module comprises three uniformly distributed air chambers and a tube slot, and by introducing constraints from fiber-reinforced structures, each leg possesses planar mobility. To achieve control of the soft mechanical legs, this study establishes both the forward and inverse kinematics of the soft legs, and tests and fits the relationship between input chamber pressure and chamber extension length. To further enhance the performance and stability of the mechanical legs, we construct an experimental platform for the MPSTR, testing the translational capabilities of a single soft leg along the X and Y axes, and analyzing the feasibility of coordinated tripod locomotion and rotation gait planning.