The floating of the shield segment will cause the segment to be misaligned and damaged, reducing the overall structural strength, waterproof performance and service life of the tunnel. On the basis of establishing the force model of the segments, by analyzing the force state of the segments, a theoretical calculation model of the segments floating is established. Taking the shield tunneling section ventilation shaft No.3-Caoqiao Station of Beijing Metro's New Airport Line as the engineering background, the abnormal rise of the segment was analyzed. By improving the performance of the synchronous grouting slurry, the floating amount of the tube segment was effectively controlled. And the slurry characteristics before and after the improvement were tested. Finally, based on the results of the slurry test and the theoretical calculation model, the floating volume of the tube segment was calculated. The results show that the theoretical calculation result of segment floating volume is consistent with the actual measured value. The theoretical calculation model in this paper has good accuracy. The segments float up a lot in a short time after it is released from the shield tail. Shortening the setting time of the slurry and improving its early strength are effective measures to control the floatation of the segments.