function loadswf(url) {
       i=_root.getNextHighestDepth();
       toget = "mc_"+i;
       _root.createEmptyMovieClip(toget,i);
       _root.toget.loadMovie(url);
       trace(toget);
       trace(toget.getDepth());
}
_root.loadswf("main.swf");

_root[toget]

谢谢楼上。另发正确版本
function loadswf(url) {
       i=_root.getNextHighestDepth();
       toget = "mc_"+i;
       _root.createEmptyMovieClip(toget,i);
       _root[toget].loadMovie(url);
       trace(toget);
       trace(toget.getDepth());
}
loadswf("main.swf");
或
function loadswf(url:String, hx:Number, hy:Number) {
       var my_mcl = new MovieClipLoader();
       var mcllistener = new Object();
       var container = this.createEmptyMovieClip("container"+this.getNextHighestDepth(), this.getNextHighestDepth());
       container._x=hx;
       container._y=hy;
       my_mcl.loadClip(url,container);
}
loadswf("test.swf",-100,0);

最好选择相对路径，绝对路径在自定义函数里面很多时候会出现意想不到的路径问题。