Abstract: Hydraulic capsule pipeline refers to the new type of transportation for goods in hollow containers in low carbon and environment-friendly way, particularly for agricultural products. Specifically, the farm products were sealed in airtight containers for point-to-point transportation through fixed pipelines, where the water pressure was taken as the power. Since the guide vanes are added around the capsule body, the water flow will generate circumferential velocity. Therefore, the length of guide vanes inevitably poses a great influence on the distribution and size of circumferential velocity. In this study, experimental and theoretical analysis was used to investigate the velocity characteristics of spiral flow in the cross section of the capsule with the length of the guide vane as the control variable. The results show that the axial velocity distribution of each cross-section was all the same with different lengths of guide vane. Specifically, the fluctuation of axial velocity decreased in each section between capsules, indicating the more uniform distribution of axial velocity, with the increase in the length of the guide vane. There was no major change in the axial velocity, but positive and the same as the water flow direction, with the increase in the length of the guide vane. Furthermore, the circumferential velocity gradient along each section between capsules first decreased, and then increased with different guide vane lengths, while the maximum and minimum circumferential velocity appeared near the upstream capsule. More importantly, the length of the guide vane presented the greatest influence on the circumferential flow velocity. The circumferential flow velocity increased with the increase of guide vane length, with a maximum of up to 1.2 m/s. The value of circumferential velocity was positive or negative, indicating that the circumferential velocity was divided into two directions, clockwise and counterclockwise along the circumference. The radial velocity gradient was the largest in the area near the upstream capsule, while smaller in the middle section between capsules under different guide vane lengths. There was a gradual decrease difference between the maximum and minimum radial velocity in the same section, where the radial velocity value was more uniform, with the increase of guide vane length. Compared with the circumferential velocity, the radial velocity was less affected by the length of the guide vane, and the radial velocity was positive or negative, indicating that the radial velocity was directed to the center of the circle and away from the center of the circle. The axial, circumferential, and radial velocity distribution on the same measuring ring was wavy under different guide vane lengths, ranging from -1.2 to 3.5 m/s, -0.6 to 1.2 m/s, and -1.6 to 1.2 m/s, respectively. The axial, circumferential, and radial velocity values were at the polar angle of 60°, 180°, and 300°. The peak value appeared at all the positions. The finding can provide a strong theoretical basis for the optimal design of capsule pipeline hydraulic transportation.