Expanding and contracting system of protective net

The present invention provides an expanding and contracting system of protective net, which comprises two support racks, a protective net, and a power device. Each support rack has a front and a rear support posts, a first cable, a second cable, and a plurality of sliding members. The two ends for the first and second cables are respectively configured on the front and rear support posts. The second cable can be pulled to move. The first and second cables are penetrated through each sliding member. Those sliding members may slide relative to the first cable. The protective net has two opposite sides, a front edge, and a rear edge. The two sides are respectively connected with the sliding members. Both ends of the rear edge are respectively fixed on the two rear posts. The two sliding members located at both sides of the front edge of the protective net are respectively fixed on the two second cables. The power device is used to pull the two second cables.