方式一：

 // -------------------------------------加载时展开所有节点
    function expandAll() {
        var zTree = $.fn.zTree.getZTreeObj("moduleTree");
        expandNodes(zTree.getNodes());
    }
    function expandNodes(nodes) {
        if (!nodes) return;
        var zTree = $.fn.zTree.getZTreeObj("moduleTree");
        for (var i=0, l=nodes.length; i<l; i++) {
            zTree.expandNode(nodes[i], true, false, false);
            if (nodes[i].isParent && nodes[i].zAsync) {
                expandNodes(nodes[i].children);
            } else {
                goAsync = true;
            }
        }
    }

            方式二：

// zTree加载时展开所有节点
function zTreeExpandAll(treeId,flag) {
expandFlag = flag ;
var treeObj = $.fn.zTree.getZTreeObj(treeId);
var nodes = treeObj.getNodesByFilter(function(node){ //自定义过滤条件
return ( node.isParent == true); //check_Child_State 用来判断是否有子节点,0表示有，-1表示无
});
if (nodes.length>0) {
$.each(nodes,function(key,value){
//[节点数据][展开/折叠][全部子孙点/当前节点][设置焦点][执行回调函数？]
treeObj.expandNode(value, expandFlag, true, false,false);
}) ;
}
}