Real train impact tests are so expensive that it is usually unrealistic to carry them out, whereas scaled model impact tests can significantly reduce the cost and are easier to conduct. This paper reports a three-dimensional scaled similitude rule for train collision. Based on the consistency of acceleration, the scaling factors of mass, velocity, time, displacement, moment of inertia, angular displacement, angular velocity, and angular acceleration between full scale and scaled models are identified. A three-dimensional simulation model for train-to-train collision is established to analyze the dynamic response between full-scale and scaled models under the condition of eccentric impact. Our results show that through multiplying the corresponding scale factors, dynamic responses of the scaled model are identical to that of the full-scale model. Thus, the three-dimensional similitude rule proposed in this paper is verified numerically and is able to guide scaled model tests in laboratory.