Objective To study the changes in lower limb muscle strength and gait after long-distance load marching of the soldiers, and investigate the effects from muscle fatigue of lower limbs on walking and running gait. Methods After fifteen male soldiers completed a 15 km marching with 17.5 kg load carriage, the isometric muscle strength of the hip, knee, and ankle joints under flexion and extension were tested, and the walking and running gait parameters were collected with Vicon motion capture system and AMTI force platform. Results After load marching, the peak moment of the hip decreased significantly (P<0.05); the mean power of the right knee decreased significantly (P<0.05); and the relative peak moment and mean power of the ankle plantarflexion decreased significantly (P<0.05). During walking, there was a significant decrease in the left hip flexion, knee flexion and extension, ankle dorsiflexion, and inversion angles (P<0.05), along with a significant increase in the knee inversion angle (P<0.05). Additionally, there was a significant decrease in the moment of the left hip flexion, knee flexion, ankle plantarflexion, and bilateral knee inversion (P<0.05), coupled with a significant increase in the moments of the right hip extension and vertical ground reaction forces (P<0.05). During running, there was a significant decrease in the step frequency (P<0.01) and an increase in the left step width (P<0.05). The left knee flexion angle and right ankle dorsiflexion angle both significantly decreased (P<0.05), while the knee adduction angle significantly increased (P<0.05). Additionally, there was a significant decrease in the moment of the bilateral hip flexion, left knee flexion, right ankle dorsiflexion, and knee adduction (P<0.05), and a significant increase in the ground reaction force at right side (P<0.05). Conclusions Lower limb muscle strength would decrease after long-distance marching, especially in the hip joint. The hip drive mechanism was used in walking gait after marching, but knee hyperextension and knee valgus would occur due to the decreased muscle strength. The ankle joint was used more during running, increasing the risk of ankle injury. To optimize gait, increase load capacity, and prevent injury, it is necessary to strengthen the hip joint and hamstring muscle groups.