Ballastless track is widely used in high-speed railway in China. Because of its good quality and small amplitude of irregularity, it is difficult to distinguish line sections when using the current track quality index (TQI) to evaluate track smoothness, which is not conducive to the fine management of ballastless track. Therefore, a new method for calculating TQI value based on the combination of amplification factor and different weight combinations is proposed. Taking the irregularity detection data from Shanghai-Hangzhou high-speed railway uplink as an example, the weight of each single component in TQI is allocated by using the coefficient of variation, and the single component value is graded according to the management standard by using the amplification coefficient. By comparing the new TQI value with the original TQI value, the calculation results of the new TQI value are divided into four intervals, TQI≤600, 600＜TQI≤700, 700＜TQI≤800, TQI＞800, in order to better evaluate and manage the smoothness of high-speed railway ballastless track.