Based on Bell polynomials, the bilinear form of variable-coefficient Gardner-KP equation is constructed. Single, double and multiple solitary wave solutions of the equation are obtained using the perturbation expansion method, and the characteristics of single solitary wave are analyzed. Based on the bilinear equation, Ba ¨cklund transformations of Bell polynomials with parameters and bilinear form of the variable-coefficient Gardner-KP equation are derived.