The transmission error of the gear transmission system is the main factor affecting its transmission performance. The expansion of special applications of elliptic gear transmission system and the improvement of transmission accuracy requirements put forward higher requirements for its transmission performance. Although many works have been presented to study the transmission error of cylindrical gear transmission system, a few works were focused on the transmission error of elliptic gears for the reason of the inconsistency of the tooth profile of the elliptic gear pair, the difficulty of establishing a transmission error model and obtaining the dynamic backlash. To overcome this problem, the theoretical model of the transmission error and backlash of the elliptic gear pair is proposed and established based on the meshing line incremental method. The ellipse gear transmission test-rig is built and the transmission test is carried out on it. Finally, the correctness of the theoretical model is verified. The results show that the dynamic backlash of the elliptic gear pair can be obtained through the bidirectional transmission error curve. The dynamic transmission error has a negative correlation with the speed and has a positive correlation with the load torque. The dynamic backlash shows an increasing relationship with the increase of speed and load torque. The research results of this article can provide a certain theoretical basis for the anti-backlash control of the elliptic gear transmission system and the improvement of transmission performance.