The pathogenesis of Crohn Disease (CD) is unknown, but there is evidence show that the inadequate immune response or overreaction of the immune system against food antigens or components of the commensal flora involve it. Corticosteroid therapy is effective for adult patients with CD, but it has side effects and can't promote mucosal healing. In recent years, Enteral nutrition (EN) is becoming primary therapy in induction and maintenance remission of CD, especially in children. But the mechanism of EN in induction and maintenance remission of CD is still unclear, and parts of patient have good clinical response to EN therapy while other don't. So we design the study to explore whether EN treats CD by effecting intestinal flora and whether the intestinal flora of patient with CD relates with clinical response.

The pathogenesis of CD is unknown, but there is evidence show that the inadequate immune response or overreaction of the immune system against food antigens or components of the commensal flora involve it. Corticosteroid therapy is effective for adult patients with CD, but it has side effects and can't promote mucosal healing. In recent years, EN is becoming primary therapy in induction and maintenance remission of CD, especially in children. But the mechanism of EN in induction and maintenance remission of CD is still unclear, and parts of patient have good clinical response to EN therapy while other don't. So we design the study to explore whether EN treats CD by effecting intestinal flora and whether the intestinal flora of patient with CD relates with clinical response.

Inclusion Criteria:

1. Patients should be in the age range of 18 - 75 years;
2. Patients should have clinical, imaging, endoscopic and histological diagnosis of CD based on WHO criteria
3. Patients should have a CDAI score of more than 150 and have a CRP level of more than 10mg/L at enrollment;
4. Patients will not be excluded if they have received 5-ASA(Aminosalicylic acid) or immunomodulator for >8 weeks and the dose is stable
5. Informed consent

Exclusion Criteria:

1. Patients who can't tolerate enteral nutrition because of complications, such as complete intestinal obstruction, gastrointestinal perforation or bleeding etc.
2. Patients who receive corticosteroids or enteral nutrition or prebiotics /probiotics/synbiotics/antibiotic treatment in the previous 4 weeks.
3. Patients who accompanied extra-intestinal manifestations, serve complications, and active perianal disease and need other drug therapies.
4. Patients who had ostomy or colectomy or subtotal colectomy
5. Patients with end-stage disease or is expected likely to die during the study
6. Patients are participating in other clinical trials or participated within 6 months prior to this study