Higher-order vortex light field generated through the process of nonlinear frequency conversion gets the researcher′s attention, but the most researches on this field concentrate on Laguerre-Gaussian beams rather than the nonlinear frequency conversion process of composite vortex. The process of frequency doubling of composite vortex is analyzed theoretically, and the vortex distribution of frequency doubling light field is obtained. Via theoretically studying, the topological charge conservation in the frequency doubling process of composite vortex is demonstrated. The topological charge conservation of Laguerre-Gaussian vortex light in the frequency doubling process based on nonlinear potassium titanyl phosphate optical crystal is experimentally demonstrated. Furthermore, composite vortex light is generated based on Mach-Zenhder interferometer, and its frequency doubling process is studied. Experimental results confirm the topological charge conservation in the frequency doubling process of composite vortex light.