The performance of a high precision bearing is closely related to surface quality of the bearing balls. Surface precision rapid detection is critical in ensuring quality of bearing balls, hence a new sphere full unfolding method applicable to in-situ optical inspection was proposed. Several sphere full unfolding methods having been proposed in recent published journals were analyzed, their shortcomings in practical applications were pointed out, unfolding principle of new unfolding device was analyzed, and theoretical analytical derivation was done. A model was developed for the new unfolding device. Adams simulation was carried out for the model. The influence of different parameters on inspection trajectory of sphere full unfolding was investigated by setting different simulation parameters. The coverage rates of meridian inspection and spiral inspection were compared. The new unfolding device could achieve full unfolding of a sphere with uniform coverage. Such device was well suited for inspection methods with small optical spots, such as in laser scattering and laser interference. The full coverage time was affected by precession velocity and rotational speed. Provided with constant precession velocity, the higher the rotational speed of main axis was, the higher the spiral interval was, full coverage time remained the same. Provided with constant rotational speed of main axis, the higher the precession velocity was, the lower the spiral interval was, the shorter the full coverage time was. Provided with simulation time of 15 s, rotational speed of main axis of 400 (°)/s, the optimum precession speed was 12 (°)/s. For the new sphere unfolding mechanism, spheres of different diameters can be inspected completely with uniform coverage by adjusting rotational speed and precession velocity, as well as focusing position.