Objective To observe the effects of frailty state and walking speed on kinematic characteristics of lower limb joints in older adults. Methods A total of 59 old people aged 60 and above participated in this study.The subjects were divided into non-frailty, pre-frailty, and frailty groups by the Kihon Checklist. The Xsens MVN motion capture inertial sensor was used to collect kinematic data from three groups of older adults during walking at slow, customary and fast speeds, and two-way repeated-measures analysis of variance was performed to determine the difference of kinematic characteristics between three groups of older adults walking under different frailty states and at different speeds. Results The age of frailty group was significantly older than that of nonfrailty group (P<0. 01). The maximum knee flexion angle and range of motion (ROM) of knee and ankle joints in frailty group were significantly smaller than those in non-frailty group and pre-frailty group (P< 0. 05), and the maximum plantar-flexion angle of the ankle joint in frailty group was significantly smaller than that in non-frailty group (P<0. 05). With walking speed increasing, the single support time of frailty group increased significantly (P<0. 05), the maximum hip flexion and extension angle, the maximum knee flexion angle, the maximum ankle plantar-flexion angle, the hip and ankle ROMs in three groups were significantly increased (P<0. 05), the double support time, the maximum ankle dorsiflexion angle, the knee ROM were significantly decreased (P<0. 05), and only the maximum hip extension angle, the hip ROM and the maximum knee flexion angle showed significant differences between slow speed and customary speed(P< 0. 05). Correlation analysis showed that the hip and knee ROMs were significantly positively correlated in pre-frailty group and frailty group at different walking speeds (P<0. 01),the knee and ankle ROMs were significantly positively correlated in frailty group at customary and fast walking speeds (P<0. 05). Conclusions With the change of frailty state, the sagittal plane angle of lower limb joints in older adults decreased continuously, mainly concentrating on knee and ankle joints. The synchronization between the two joints were enhanced, and the degree of freedom was decreased during walking. With the increase of walking speed, older adults under different frailty states adopted the same walking strategy. These results are helpful for screening and rehabilitation guidance of the frailty population.