In this paper, the soft sensing system that can measure foot pressure and the muscle volume is proposed. The presented system, equipped with the capability to measure foot pressure, systematically analyzes plantar pressure distribution, facilitating comprehensive gait analysis. Furthermore, the application of pneumatic-based mechanomyography (pMMG) sensors allows for concurrent measurement of quantitative muscle volume, providing a corresponding indicator of muscle activation. Three pMMG sensors to measure muscle volume and two FSR sensors to measure the foot pressure are integrated for each leg. To evaluate the proposed sensor system, experiments to compare the performance with traditional motion capture system and simulations are conducted.