Objective To observe the effects of frailty state and speed on the kinematics of lower extremity joints in the elderly. Methods 59 elderly aged 60 and above participated in this study and were divided into non-frailty, pre-frailty, and frailty groups by the Kihon Checklist. The motion capture inertial sensor was used to collect the kinematic data walking at slow, comfortable, and fast speeds, and two-way repeated-measures analysis of variance was performed to determine the difference of the kinematic characteristics between three groups of elderly walking at different frailty state and speed. Results The results showed that the age of the frailty group was significantly higher than that of the non-frailty group (P <0.01). The maximum knee flexion angle and the Range of Motion of the knee and ankle in the frailty group were significantly lower than those in the non-frailty and the pre-frailty group (P <0.05), and the maximum plantar-flexion angle of the ankle joint in the frailty group was significantly lower than that in the non-frailty group (P <0.05). With increased walking speed, the single support time of the frailty group increased significantly (P <0.05), the maximum hip flexion and extension angle, the maximum knee flexion angle, the maximum plantar-flexion angle of the ankle, the Range of Motion of hip and ankle in the three groups were significantly increased (P <0.05), the double support time, the maximum dorsiflexion angle of ankle and Range of Motion of knee were significantly decreased (P <0.05), and only the maximum extension angle of the hip, the Range of Motion of the hip and the maximum flexion angle of the knee showed significant differences between slow speed and customary speed(P <0.05). Correlation analysis showed that Range of Motion at the hip and knee were significantly positively correlated in the pre-frailty and frailty group at different walking speeds (P < 0.01), Range of Motion at the knee and ankle were significantly positively correlated in the frailty group at the normal and fast walking speeds (P < 0.05). Conclusion With the change of frailty state, the sagittal plane angle of lower limb joints in the elderly decreased continuously, mainly focusing on knee and ankle joint, the synchronization between the two joints were enhanced, and the degree of freedom was decreased during walking. When increasing walking speed, the elderly in different frailty states adopted the same walking strategy, and the results are helpful for follow-up screening and rehabilitation guidance of the frailty population.