The invention discloses an alignment system for workpiece alignment and an alignment method of the alignment system, particularly relates to an offline alignment system for workpiece alignment and an alignment method of the offline alignment system, and belongs to the technical field of machining. According to the offline alignment system for workpiece alignment and the alignment method of the offline alignment system, a base table and at least one supporting plate assembled on the base table and used for workpiece clamping are included; at least one joint arm used for workpiece alignment and a controller used for operating the joint arms to measure workpieces and displaying measuring data are further included; and the controller is connected with the joint arms. Through the adoption of the offline alignment system for workpiece alignment and the alignment method of the offline alignment system, practicality and reliability are achieved; universality is high; operation is simple; high application value is achieved; workpiece alignment and clamping work is carried out on the offline alignment system and does not need to be carried out on a machine tool workbench; the situation that a machine tool is shut down due to the fact that the workpieces are aligned and clamped on the machine tool is effectively avoided; and the utilization efficiency of the machine tool is improved.