Carbon is hard to be sensitively detected in laser-induced breakdown spectroscopy (LIBS). The optical emission can be significantly enhanced by resonantly exciting CN radicals in the plasma center using LIBS assisted with laser-induced fluorescence (LIBS-LIF). However, the nitrogen source for CN formation is provided by ambient gas. Therefore, we propose a new approach of periphery excitation in plasma to improve CN fluorescence. The optical and spatial characteristics of CN radicals in plasma were discussed. A fluorescence map was established by combining focal point location and fluorescent intensity, demonstrating that plasma periphery had 4.2 times stronger fluorescence than the center.