Aims:Prospectively observe the effects of Vitamin D drops supplementation on the chronic course of Crohn's disease patients, analyze whether the effect of Vitamin D drops on CD patients is affected by factors such as disease site, disease activity, treatment, etc.Exploring the relationship between Fok I gene polymorphism and the efficacy of vitamin D supplementation. Provide a certain theoretical basis for "precision treatment" for CD patients in the future.||Design：It is a prospective cohort study. Investigators include a total of 60 participants with CD according to the inclusion and exclusion criteria, and divide them into two groups to assess their initial disease activity and detect related indicators. At the same time，investigators detect the Fok I gene polymorphism in all participants.One group is given Vitamin D drops 400IU per day orally, and the control group do not intervene. Participants' disease activity is assessed at baseline and related indicators are determined. The disease activity is re-evaluated at 2, 6, 14, 22, 30, and 38 weeks, and the serum indexes are re-evaluated.Investigators use statistical methods to analyze whether Vitamin D drops supplementation treatment can increase the serum 25 (OH) D level of CD participants who are treated with infliximab, improve the condition of CD participants,relationship with Fok I gene polymorphism，and analyze the effects of Vitamin D drops on participants with CD is affected by factors such as disease site, disease activity, and treatment.