A severe aerodynamic load generated when two high-speed trains meet inside a tunnel can induce lateral vibration of the vehicle body. To investigate the aerodynamic characteristics responsible for such vibration, a full-scale high-speed train aerodynamic model consisting of eight car groups and a tunnel model with slab track are constructed using the improved delayed detached eddy simulation (IDDES) method. The pressure on both sides of the train body, the surrounding pressure field, the pressure distribution along the body, the pressure difference and its standard deviation for each carriage, and the time- and frequency-domain characteristics of the lateral force, overturning moment, and yaw moment are systematically analyzed. Correlation analysis among these load parameters is also conducted. The findings are as follows: (1) When two trains meet in the tunnel, the resulting pressure pulse causes abrupt changes in the body surface pressure and alters the surrounding pressure field. (2) The pressure difference between the two sides of the train increases progressively toward the tail, and its standard deviation shows that the tail car experiences the most severe fluctuation, reaching 158.51 Pa. (3) Compared with the head and middle cars, the tail car exhibits more pronounced fluctuations in lateral force, overturning moment, and yaw moment, indicating a higher susceptibility to lateral vibration. (4) The lateral force and overturning moment demonstrate a strong correlation, with a Spearman coefficient of －0.990. These results elucidate the lateral aerodynamic characteristics of high-speed trains meeting in tunnels and clarify the correlation among key load parameters.