Hi, my umbraco editor panel pop out with

.umb-editor--small

class which limited in width: 500px but I want to apply

.umb-editor--large

for better edit experience, how can I do that?

It's something that whatever triggers the editor panel needs to set. For the built-in property types in Umbraco that choice has been made for you. If it is a custom editor that opens an editorpanel then you can set the size in the options you pass to the editorService like this:

js
function openMediaPicker() {
    vm.buttonState = "busy";

    var options = {
        title: "Select image",
        view: "/App_Plugins/Kontainer/infiniteEditor.html",
        size: "large",
        submit: function(model) {
            model.forEach(function(item){
                $scope.model.value.images.push(item);
            })
            editorService.close();
            vm.buttonState = "init";
        },
        close: function() {
            editorService.close();
            vm.buttonState = "init";
        }
    };
    editorService.open(options);
}