This paper points out the problems in air conditioning and the urgent need in energy saving. By observations and analyses, it shows that the idea of making use of natural resources to improve the indoor air may date back to ancient times. This paper also examines the feasibility of taking advantage of dry or wet bulb temperature, solar energy, underground rock etc. to regulate the room temperature. Finally, it concludes that the above mentioned old idea has such characteristics as energy saving, low cost and less pollution. Therefore, it is a good green plan in energy saving air conditioning.