In this study, through the homemade nutrient solution circulation system, the system operation and stop time were set to 7.5 min (T₁), 15 min (T₂), 22.5 min (T₃), and 30 min (T₄) for 4 treatments. With the control (CK), the effects of different nutrient solution cycle intervals on nutrient solution environmental indicators and root morphology of hydroponic purple cabbage, proline, malondialdehyde content, endogenous hormones in roots and microscopic structure of root cells were studied. In order to explore the mechanism of the effect of nutrient solution circulation interval on the root growth of hydroponic purple cabbage. The results showed that: (1) during the 0th to 10th day, the dissolved oxygen content of the nutrient solution of CK decreased by 3.5 mg/L, and the dissolved oxygen of T₁-T₄ decreased by about 1.2 mg/L, and the nutrient solution of CK dissolved. The rate of oxygen decline is about 3 times that of T₁-T₄; the circulation interval of nutrient solution has no effect on the temperature of nutrient solution and the total amount of ions. (2) At the 10th day after treatment, the root morphological indexes such as total length, root surface area and root diameter of purple Chinese cabbage treated by T₁-T₄ were higher than that of CK treatment, and the roots of T₂ and T₃ grew more than that of T₁ and T₄, indicating that a certain range of nutrient solution circulation interval can promote root growth. (3) The contents of proline and malondialdehyde in the roots of purple cabbage of CK were the highest. Among T₁-T₄ treatments, the contents of proline and malondialdehyde in roots of T₂ were relatively high, and T₄ treatment was the lowest and both were significant below the control. (4) After 10 days of different treatments, there were significant differences in endogenous hormones in purple Chinese cabbage, and the contents of IAA and GA3 were consistent, both T₂>T₃>T₄>T₁>CK; the order of ABA content was CK>T₄>T₁ >T₃>T₂, and the ABA and ZR contents of T₂ are also at a minimum level. (5) Observation of cell microstructure revealed that the crosssection of the roots of CK, T₁-T₄ treatments from the inside to the outside of the third layer of cortical cells, the diameter of the new lateral roots at a distance of 1 cm from the root tip, the diameter of the vascular bundle and the xylem region accounted for the diameter of the root system. The proportions of T₁-T₄ were significantly higher than that of control, and the three indicators were the largest with T₂ (30, 450 μm, 42.22%), indicating that the root growth of T₂ is optimal. Studies have shown that the nutrient solution cycle time of 15 min (T₂) can significantly improve the dissolved oxygen content of nutrient solution, effectively increase the content of IAA and GA₃ in roots, promote the division of root cortical cells, increase the diameter of new lateral roots and the diameter of vascular bundles and xylem regions. The root system of hydroponic purple cabbage was optimally grown.