Abstract: A one-dimensional numerical model is developed in this paper to calculate the changes of temperature and moisture in the land-air coupled system. In the soil, the model uses heat and water balance principles in computations of the soil temperature and moisture.In the atmosphere, the effects of longwave and shortwave radiations, cloudiness, condensation and other factors on variations of the atmospheric temperature and moisture are taken into account. The model is tested with a kind of soil which is selected as being representative. Results show that the model can fairly simulate the diurnal variations of many physical quantities. Calculations indicate that the initial distributions of temperature and moisture in the atmosphere and in the soil have quite large influences on the results. The principles in this paper can be used for parameterizations of the land-air interaction in general circulation models.