不BB了，直接上代码

using UnityEngine;
using System.Collections;


public class Hero : MonoBehaviour {

private bool isMouseDown = false;


private Vector3 lastMousePosition = Vector3.zero;


public Transform hero;


void Start(){


}


// Update is called once per frame
void Update () {


if(Input.GetMouseButtonDown(0)){
isMouseDown=true;
}
if(Input.GetMouseButtonUp(0)){
isMouseDown=false;
lastMousePosition = Vector3.zero;
}
if(isMouseDown){
if(lastMousePosition!=Vector3.zero){
//Camera.main.ScreenToWorldPoint(Input.mousePosition)
//print (Camera.main.ScreenToWorldPoint(Input.mousePosition));
Vector3 offset = Camera.main.ScreenToWorldPoint(Input.mousePosition) -lastMousePosition;


transform.position = transform.position+offset;
checkPosition();
}
lastMousePosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
}


}




private void checkPosition(){
//check y -3.3f +3.3f
//check x -1.9f +1.9f
Vector3 pos = transform.position;
float x = pos.x;
float y = pos.y;
if(y<-3.3f){
y=-3.3f;
}
if(y>3.3f){
y=3.3f;
}
if(x<-1.9f){
x=-1.9f;
}
if(x>1.9f){
x=1.9f;
}
transform.position= new Vector3(x,y,0);
}
}

再将脚本挂在要移动的物体上，拖一下game object到Transform hero既可。

最后效果如下：