In order to grasp the variation law of secondary flow in helical tube, the local intensity and development law of secondary flow in helical tube were studied, and the dimensionless helical intensity H was proposed as the local secondary flow intensity index. By means of numerical simulation, the average volume of H Hm was taken and compared with the Dean number describing the overall secondary flow intensity. The results showed that with different Reynolds number, curvature and pitch, the correlation coefficient between Hm and Dean number was about 1, and there was a good proportional relationship, indicating that H could accurately measure the intensity of local secondary flow. At the same time, the influence of geometric parameters on the development law of secondary flow in the helical tube was explored. According to the intensity of secondary flow, the flow in the helical tube could be divided into development stage, transition stage and stable stage. The secondary flow increased rapidly in the development stage, reached its maximum value in the transition stage, and fluctuated periodically in the stable stage. The increase of Reynolds number could significantly increase the intensity of secondary flow, but could not affect the location of secondary flow three stages. The increase of curvature could slightly increase the intensity of the secondary flow and extend the distance of the secondary flow to the stable stage. The pitch had little influence on the intensity and development of secondary flow. [ABSTRACT FROM AUTHOR]