The objective of this research is to reveal time-varying mesh characteristics and nonlinear dynamics of crossed beveloid geared rotor system with small shaft angle. A new mesh model based on exact gear geometry is developed. Using the proposed mesh model, the time-varying mesh stiffness and time-varying transmission error are obtained. A nonlinear vibration model is setup to study the dynamics of crossed beveloid geared rotor system using lumped parameter method considering variation of load and backlash nonlinearity. The results show that the increase of the torque load tends to increase the transmission error, mesh stiffness, dynamic transmission error as well as dynamic mesh force. Also, the frequency of the major response peak becomes lager due to the increase of mesh stiffness. Under a light torque load level, it can be seen the rich non-linear behaviors including jump discontinuities coupled with single-sided tooth impacts and double-side tooth impacts with the increase of backlash. Under a heavy torque load level, the range of double-side tooth impact becomes wide and the dynamic mesh force increases.