Various methods, including the Q-system method, have been proposed to estimate the conditions of rocks in fields, and many researchers have quantitatively estimated the Q-values of the Q-system. Physical variables have been considered in various studies, but the accuracy of those studies has become a subject of controversy. This study investigates the conditions of a rock mass using electrical resistivity, which is strongly affected by the flow of water and the condition of the joints. The relationship between the parameters of the Q-system and the electrical resistivity was deducted using an electrical resistivity formula. The relationship between the Q-value and the electrical resistivity of the sandstone was obtained using an electrical resistivity formula as well. A correlation analysis was performed to verify the degree of correlation between the parameters of the Q-system and the electrical resistivity. This study also tried to establish stochastically the relationship between the parameters of the Q-system, possible to existing in reality, on the basis of field data.