In order to figure out the velocity distribution and resistance loss of serpentine curved tunnel, based on Paomashan No. 1 tunnel project, numerical calculation method is used to simulate the velocity distribution and resistance loss in serpentine curved tunnels with different curvature radius and different inversion. Calculation results show that: (1)There is a significant transition stage of both velocity distribution and resistance loss in serpentine curved tunnel as entering the reverse curved tunnel; the length of transition stage is about 450 m. (2)The velocity distribution shifts from the right side (inside) to the left side in transition stage; the resistance loss of transition stage decreases first and then increases. (3)When the radius is small,the resistance loss calcalated in transition stage is obviously smaller than that in the specification; when the radius is greater than 1 200 m, the two calcalation results show little difference.