Almost all the cracks in mass concrete are surface cracks. Full-section cracks and deep-level cracks are mainly developed from early surface cracks. This paper describes the characteristics of the surface cracks of mass concrete firstly. Then a semi-infinite plane model for surface temperature calculation is compared with infinite model. The temperature of surface zone in mass concrete under different boundaries is controlled by semi-infinite model, and is transferred to and calculated by an equivalent infinite model under certain conditions. If the temperature declining duration of air is no more than the critical time when the disturbed front perforates half-thickness of the infinite plate, it may be expressed as multi-line process approximately, and most importantly the temperature in surface zone of concrete can be calculated with the formula educed by infinite model. With 400 mm × 400 mm × 220 mm concrete specimens, the temperatures in surface zone are experimentally researched under outside environment, which has attested the method presented. It is also found that the new method to describe declining process of air temperature is more accurate than the method prevailing, and there does exist an opportunity to develop a physical model for the temperature process of mass concrete within a short period of time.