The invention relates to a cobalt cross-linked composite carbon aerogel with an adjustable pore size, and a preparation method thereof, wherein a cobalt salt and a mixture of polyamide acid and graphene oxide are cross-linked to obtain an aerogel, and the aerogel is carbonized to obtain the composite carbon aerogel. The preparation method comprises: preparation of a graphene oxide/polyamic acid hydrogel, preparation of a cobalt salt/graphene oxide/polyamic acid hydrogel, preparation of a cobalt salt/graphene oxide/polyamic acid aerogel, and preparation of a cobalt cross-linked composite carbonaerogel. According to the invention, the aerogel of the invention has high specific capacity and excellent rate capability; and the method is simple in process and simple to operate.