The shape-shifting robot AMOEBA-I has a variety of configurations and the turning ability of robot in different configurations is largely restricted by the environmental conditions. The turning performance of evaluation is done by qualitative manner and the result of evaluation is vague in recent years. The turning performance of evaluation by quantitative manner is proposed in this article. Through establishing the mathematical models of the influenced factors, the energy, space, time and angle velocity which influence the efficiency of turning performance are analyzed. The algorithm based on the combination between subjective and objective methods is researched to certain the coefficients of the factors. Finally, the performance of robot turning is curtained by computed and simulation which can satisfy the requirements of turning algorithms in different environment.