In this paper, natural polysaccharides sodium alginate (SAL) and chitosan (CS) are used as basic raw materials, and CaCl2 is used as a cross-linking agent. The sodium alginate solution is dropped into the chitosan-calcium dispersion solution. While physical crosslinking occurs between the sodium alginate and the chitosan molecular chain, it is also simultaneously crosslinked with calcium ions, the millimeter-grade chitosan-calcium-sodium alginate (CS-Ca2+-SAL) hydrogel with a sphere plastic form was prepared by one-step method. The hollow Gel spheres with smooth surface, uniform shape and shell were successfully prepared by adjusting the amount of raw materials, the speed of the centrifuge, the diameter of the needle and the crosslinking method. Using fluorescent carbon nanodots as label, the swelling properties and slow-release properties of Gel spheres were investigated. The results show that the swelling performance of the hydrogel spheres is significantly affected by pH. The swelling rate is the smallest when the solution is at pH = 1.2, and the swelling rate is the largest when it is at pH = 6.8. The experimental results of release rate of fluorescent carbon nanodots in pH=7.1 Tris-HCl buffer solution indicate that the release mechanism is fitted to Hixcon-Crowell models and it conclude that the Gel sphere has the dissolution sustained release process, accompany with diffusion of nano-drugs.