use [DllImport("xxxx")] for .so with other .so

it success for just only one .so(with funtion add(a,b){return a+b}) but, if this one .so(with function add(a){return a+getSomeThing()}) has use other .so(with function getSomeThing(){return 5}) ,it is not work,said "DllnotfoundException" , how should i do , emm~~ i ask for something before ,but here has no one reply me .. i hope this will change,thanks a lot~