Objective To monitor the exercise load in daily life activities, a reliable method to estimate the real-time plantar pressure based only on a few sensors was presented. Methods Pedar-X pressure insoles were applied to collect plantar pressures from 10 healthy young adults performing 5 typical motions (vertical jump-landing, level walking, level running, stair ascending and stair descending). Stepwise linear regression was performed to reconstruct a mathematic model of calculating the foot force for each style of the motion based on 99 individual pressure data. Then these models were validated by comparing the plantar pressures measured by Pedar-X system and the estimated values by these models when other 4 subjects conducted the same 5 motions and the continuous motion composed of the 5 motions. Results Regardless of the single motion or continuous motion, the foot force calculated by each model for each motion, as well as that calculated by level walking model for each motion were almost the same as the data measured by Pedar-X system. In addition, there was no significant difference between the estimated values by each motion model and level walking model. Conclusions The foot force in daily life activities can be monitored effectively by level walking model with only 5 pressure sensors placed under T1, M2, M3, HM and HL region of the foot.