Disclosed in the present invention is a support capable of fully-automatically performing rotary clamping by means of linkage between a gear and a rack. The support includes a back side base, a bottom supporting arm, a left-side gripping arm and a right-side gripping arm. A left-side vertical spur rack portion and a right-side vertical spur rack portion are disposed on the left and right sides of the bottom supporting arm. A left-side gear engages with the left side of the left-side vertical spur rack portion, and a right-side gear engages with the right side of the right-side vertical spur rack portion. An inner end of the left-side gripping arm is connected to the left-side gear, an inner end of the right-side gripping arm is connected to the right-side gear, the left-side gripping arm rotates with the left-side gear, and the right-side gripping arm rotates with the right-side gear.