一、新建两个脚本

using UnityEngine;
using System.Collections;

[ExecuteInEditMode]
public class UILabel : MonoBehaviour {

    [HideInInspector]
    [SerializeField]
    public string text;

    void OnGUI()
    {
        GUI.Label(new Rect(0, 0, 200, 200), text);
    }
}

using UnityEngine;
using UnityEditor;
using System.Collections;

[CustomEditor(typeof(UILabel))]
[CanEditMultipleObjects]
public class UILabelInspector : Editor
{
    protected UILabel mLabel;

    protected virtual void OnEnable()
    {
        mLabel = target as UILabel;
    }

    public override void OnInspectorGUI()
    {
        string text = EditorGUILayout.TextArea(mLabel.text, GUI.skin.textArea, GUILayout.Height(100f));
        if (!text.Equals(mLabel.text)) { mLabel.text = text; }
    }
}

1.把UILabel脚本挂在一个GameObject上

2.UILabelInspector脚本必须放在Editor目录下

工程结构

编辑效果