The invention provides a silk ligament and a preparation method thereof, and relates to the field of prosthetic materials. The silk ligament is prepared from natural silk serving as raw materials by stranding, twisting, degumming and bone morphogenetic protein (BMP) filling, and consists of lead wires (1), an inner core (2) and a core shell (3), wherein the lead wires (1), the inner core (2) and the core shell (3) are formed by weaving integrally; the core shell (3) is fixed on the middle part of the inner core (2); and the lead wires (1) are fixed at both ends of the inner core (2). Compared with the conventional artificial ligament, the mechanical property of the silk ligament are in stricter accordance with the properties of anterior cruciate ligaments (ACL) of human bodies, and after being filled with the BMP, the silk ligament rebuilding is more convenient.