A novel sodium alginate-based Pd-3D double network hydrogel Pd/Ca-Alg-PAAS has been fabricated and successfully applied in the selective hydrogenation of phenol for the first time. The prepared catalyst showed excellent catalytic activity and high selectivity (99.8%) for cyclohexanone in the selective hydrogenation of phenol. Furthermore, this double network hydrogel of Pd/Ca-Alg-PAAS still kept a conversion of over 80% with the selectivity for cyclohexanone being over 99% after 6 runs, superior to the single network hydrogel of Pd/Ca-Alg. TEM and FT-IR results demonstrated that the Pd species were highly dispersed in Pd/Ca-Alg-PAAS, and the addition of sodium polyacrylate could enhance the interaction between hydrogel and Pd2+ and thus inhibit the agglomeration and loss of the active Pd species, accounting for the good stability of Pd/Ca-Alg-PAAS.