The object of this study is to investigate the fundamental characteristics of the rhisosphere environment control by means of the digital computer.In this paper, as the first report, the fundamental characteristics of the soil temperature control system by means of the digital computer are being discussed.A mathematical model of the controlled system was derived on the basis of the indicial response experiment. Then, solutions of the mathematical model were obtained by means of the digital computer. The simulated indicial response well fitted to the experimental data.As a result, the state equations, represented by simultaneous first order linear ordinary differential equations with respect to time on the basis of the heat conduction partial differential equation and its matrix exponential type state transition solutions, were found suitable as a mathematical model of the controlled system.Thus, a mathematical model to be used for the soil temperature control by means of the digital computer was obtained and it was confirmed that the indicial respose method is appropriate for identifying the parameters in the model.