Abstract: The tooth profile equation and tooth profile interference of a type of two-tooth difference steel ball movable tooth transmission were studied. The transmission principle and mesh-pair structure of the transmission equipment were analyzed,and the tooth profile equations of the closed grooves on moving and fixed discs were established based on the rotational speed conversion and envelope theory. The main curvature and main curvature radius formulae of the closed groove tooth profile on the fixed disc were deduced. The design condition of no tooth profile interference appearance on the closed groove of the fixed disc was put forward through the tooth profile interference and its occurring characteristics were investigated. The equations and results can be adopted as the analysis basis and foundation for tooth profile designing and manufacturing of the two-tooth difference steel ball movable tooth transmission equipment.