The invention discloses a rotary base plate tracking sun automatically and belongs to the technical field of solar power generation and heat utilization. The rotary base plate comprises a base, a horizontal rotary mechanism and the like, wherein the horizontal rotary mechanism comprises a horizontal rotary support, a drive gear, a speed reducer, a direct current motor and an automatic controller;the horizontal rotary bearing is mounted on a flange block of the base; the drive gear is fixed on the output shaft of the speed reducer and meshed with a moveable gear ring of the horizontal rotary bearing; the speed reducer is fixed on the base; the input shaft of the speed reducer is connected with a direct current motor; the automatic controller is connected with the direct current motor; thedrive gear, the speed reducer and the direct current motor are positioned on the same vertical line; main and auxiliary stand columns are symmetrically arranged on the moveable gear ring; and an illuminator bracket base is positioned on the upper ends of the main and auxiliary stand columns. In the invention, the base flange is connected with the horizontal rotary bearing in a large round disc shape, so the rotary base plate has a high bearing capability, the illuminator bracket base has high stability, and the wind and snow bearing capability of the rotary base plate is high.