Abstract: An artificial knee joint includes a four-bar linkage, an extension bar having a first end pivotally connected to the four-bar linkage, and a restoring device connected to a bottom of the four-bar linkage and comprising a transmission rod having a first end pivotally connected to and retractably moving a second end of the extension bar. The four-bar linkage includes a first, second, third, and fourth connecting bar, any two adjacent connecting bars of which are connected together by their respective pivot axles. When the four-bar linkage is moved to a locked state, a specific included angle is defined between any two adjacent straight lines joining adjacent pivot axles of the four-bar linkage. While walking, an artificial leg of an artificial limb using the artificial knee joint does not produce unexpected wobbles in the swing phase, and the artificial limb can provide enough support in the stance phase.