The key of the research on SHG cones is its phase-matching condition. By way of substituting the phase-matching of noncollinear SHG for the cross-over of its correspondent refractive-index surfaces, we have successfully given the characteristics of SHG cones in uniaxial crystals, the reason for its occurenoe, its change-rule, its relevant formulations, and its application such as determining crystals optics axis, monitoring crystal s main-plane, and realizing the optimization of crystal collinear SHG.