The gear involute artefact (GIA) is the benchmark for the trace of involute gear profile deviation and the value-transmission of involute profile. It is the standard for calibrating the instruments for measuring gear involute profile. However, there is no class-1 GIA that can meet Chinese national standard of GIA GB/ T 6467- 2010 at present. Requirements of the evaluation range and profile form deviation of class-1 GIA are extremely strict. The arc length within the non-evaluation range of the tooth root is only about 0. 1 mm, which is easy to be affected by the machining error. It may result in undercutting or incomplete machining of the tooth root. Then, the tolerance of profile form deviation is exceeded. In this article, the mathematical model of the relationship between the initial rolling angle error and the involute profile deviation at the tooth root is formulated. The reason for the out of tolerance of the profile form deviation at the tooth root is analyzed, and the model is verified by the Siemens NX motion simulation and CAD simulation. Based on the above model, a machining method for tooth root at GIA with gradually modified is proposed, and a new kind of GIA with three base circle parameters is processed by the proposed method. The profile form deviations f fα < 1 μm within the evaluation range of four teeth are processed, which meets the requirements of Chinese national standard of GIA GB/ T 6467- 2010 for the evaluation range and the profile form deviation of class-1 GIA. This research provides a process method support for the precision manufacturing of class-1 GIA.