Recently, Minimally Invasive Surgery(MIS) has come to the front. The research on surgical robot for operational support has been actively done. To use such robots in MIS, it is needed to estimate the environmental impedance as the numerical data and to preserve it as the standard reference value of the safety field of internal organs. In this paper, the environmental model considering nonlinear stiffness in real environment by bilateral control is proposed. The proposed method can estimate environmental model without depending on the initial position of a slave system and environmental surface. To verify the viability of the proposed method, experimental results are shown.