The tooth profile form deviation of class-1 gear involute artefact is evaluated from roll path length 3 or 5 mm starting with the base circle according to the Chinese national standard for gear involute artefact. The arc length corresponding to the involute is only 0. 03~ 0. 18 mm, making the root of the involute tooth profile of class-1 gear involute is difficult to be measured. To exploit the accurate transmission of the value with class-1 gear involute artefact better, the special structure of class-1 gear involute artefact and the effect of the probe radius on the measurement results of the involute profile deviation is analyzed. The following conclusions are drawn. Firstly, the measurement error introduced by probe radius increases with increasing probe radius and decreasing rolling length as the rolling angle error at the root of involute is considered, and the measurement error near the base circle can reach 50% ~ 200% of the tooth profile deviation. Secondly as the error in the machining of the involute tooth surface is considered only, the measurement error introduced by probe radius and the affected range of rolling length increases with increasing probe radius and the base radius of the involute being measured, and the measurement error is about 10% ~ 60% of the profile form deviation within the range of 10% of roll path length at the tooth root. The conclusions above are verified by measuring the same gear involute artefact with probe radius rp = 0. 5 and 2. 5 mm. The basis for the ultra-precise manufacture, measurement and the selection of the roll path length to be used of class-1 gear involute artefact is provided.