The invention discloses a testing system of a plate high temperature forming limit diagram. The testing system comprises a biaxial drawing device, a material heat/force simulation testing device and a measurement analysis device, wherein the biaxial drawing device is used for carrying out drawing deformation on a sample after the sample is heated by the material heat/force simulation testing device; the measurement analysis device is used for obtaining sample deformation data and analyzing and calculating the sample transformation data so as to obtain the plate forming limit diagram. According to the testing method of the plate high temperature forming limit diagram, by designing the biaxial drawing device and corresponding samples at different strain states, the temperature and the strain velocity of a sample transformation area can be controlled accurately by using the material heat/force simulation testing device; and moreover the deformation area is free from friction during the drawing process; the operation is simple; the forming limit diagrams under different temperatures and strain velocities of a plate can be obtained; and important references are provided for process design and mold design in the plate tepidity forming technology.