Objective To explore the coordination and coordination variability of lower limbs in patients with functional ankle instability (FAI) during level ground walking. Methods Fifteen male subjects with right FAI (FAI group) and 15 healthy male subjects (control group) were recruited to walk on the ground at a self-selected speed. The kinematic data of 5-minute walking were collected using Qualisys infrared high-speed optical motion capture system. The coupling angle and the standard deviation of the coupling angle between the lower limb joints were calculated by using Matlab software to write codes. Circular distribution data were used for coupling angle statistics, and an independent sample t-test was used for the standard deviation of coupling angle. Cohen’s d was used to evaluate the effect size. Results The coupling angle of the hip-knee joint at sagittal plane in FAI group was larger than that in control group in the first half of the middle stance and the last quarter of the swing phase. The coupling angle of the hip-ankle joint at sagittal plane in FAI group was also larger than that in control group before the terminal stance. The coupling angle of the knee-ankle joint at sagittal plane in FAI group was lower than that in control group in the second half of middle stance and the first half of the terminal stance. The coupling angle of the hip-ankle joint at coronal plane in FAI group was smaller than that in control group in the loading response stance and the last quarter of the swing stance. The standard deviations for coupling angles of the hip-ankle joint at coronal and sagittal plane in FAI group were higher than those in control group at the terminal and pre-swing stances. Conclusions The gait pattern of FAI patients differs from that of healthy people. The mode of coordination shows a compensatory protection strategy. The greater coordination variability in the terminal stance and pre-swing suggests that the changes in ankle sensory perception in FAI patients lead to adaptive changes in motor control of the hip, knee, and ankle joints.