The pin-rack gearing is a particular type of cycloidal gearing which transforms a rotation motion to a linear one. Comparing with rack and pinion gearing and hydraulic swing cylinder, the pin-rack gearing has a more compact structure, less mass and lower cost. Nevertheless, designers always worry about vibration, noise and low use life as pin-rack mechanism working caused by deficiency of design theory. The present research derived the pin-rack gearing tooth profile equation and studied the geometry relationship among design parameters. The results can help to improve the pin-rack gearing design.