The carrying capability and the service life of a four-point-contact slewing bearing are influenced significantly by its raceway geometry parameters. In this paper, the carrying capability is characterized by the maximal contact stress in the paper. The usual industry practice is to specify the service life as the $L_{10}$ life. The geometry parameters, cross section clearance, ratio of curvatures, rolling ball diameter, and initial contact angle, are also considered. The sensitivity of each parameter influencing the carrying capability and the service life is discussed as well. The results show an interesting phenomenon, indicating that the maximal contact load and the maximal stress do not always have the same varying trend when discussed parameters vary. The developed design can be utilized as a reference for an optimal slewing bearing design. If a slewing bearing of high static carrying capability is required, it can be designed with large ratio of curvatures and rolling ball diameter. In terms of service life, the cross section clearance and the initial contact load should also be considered.