Althoung smart phones are very useful, they have some disadvantage. So we should use smart phones smartly. Firstly, we should not use smart phones too long. That makes our eyes weaker and we do not have time for outdoor activities. Secondly, we should only use smart phones for useful things. We can look up English words, listen to music or contact with friends such as send emails. Thirdly, we should not use smart phones to watch bad websites and play computer games. Fourth, we should use smart phone in a short time to travel about the world which we don’t know about the world. In short, we must use smart phones smartly.