The invention discloses an automatic conveying system of a large equipment coating line. The automatic conveying system comprises a workpiece storage rack, a stored program control conveying machine, a roller machine conveying machine and a friction power and free chain conveying line. A sling transport rack is connected to the workpiece storage rack and connected with a workpiece bracket. The top of the sling transport rack is provided with an upward-extending hoisting branch arm, and the lower portion of the sling transport rack is provided with a suspension rack. The hoisting branch arm is provided with an outward-extending hoisting arm. A limiting groove is formed in the hoisting arm. Two suspension arms are arranged on one side of the suspension rack and provided with opposite suspension grooves. A workpiece suspension arm is arranged on the workpiece bracket. A stored program control suspension arm is arranged on the stored program control conveying machine and provided with a stored program control bracketing arm. The friction power and free chain conveying line is provided with a friction conveying base. The bottom of the friction conveying base is provided with a power and free chain suspension arm. The automatic conveying system can continuously transport large workpieces from electrophoresis to coating, and has the advantages of being high in transport efficiency, small in occupied area and accurate in reaching position.