The patients with Crohn's disease (CD) are often accompanied with nutritional deficiencies. Compared with other intestinal benign disease, patients with CD have the higher risk of developing postoperative complications following intestinal resection. The aim of this study was to investigate the risk factors for postoperative infectious complications (PICs) after intestinal resection for CD, as well as search a practical preoperative nutritional index for PICs in patients with CD. A total of 122 patients who underwent intestinal resection for CD during 2011 to 2015 were retrospectively analyzed. After operation, 28 (22.95%) patients experienced PICs. Compared with the non-PICs group, the patients with PICs have the lower preoperative body mass index (BMI) (16.96 ± 2.33 vs 19.53 ± 2.49 kg/m2, P < .001), lower albumin (ALB) (33.64 ± 5.58 vs 36.55 ± 5.69 g/L, P = .013), higher C-reactive protein (CRP) level (30.44 ± 37.06 vs 15.99 ± 33.30 mg/L, P = .052), and longer hospital stay (22.64 ± 9.93 vs 8.90 ± 4.32 days, P < .001). By analyzing the receiver-operating characteristic (ROC) curve, BMI have better value in predicting the occurrence of PICs than ALB. The areas under the ROC curves of BMI for PICs was 0.784 (95% confidence interval 0.690–0.878, P < .001) with an optimal diagnostic cut-off value of 17.5 kg/m2. In the univariate and multivariate analysis, BMI < 17.5 kg/m2 (P = .001), ALB < 33.6 g/L (P = .024), CRP ≥ 10 mg/L (P = .026) were risk factors for PICs. Patients with a lower preoperative BMI (BMI < 17.5 kg/m2) had a 7.35 times greater risk of PICs. Therefore, preoperative BMI could be regarded as a practical preoperative nutritional index for evaluating the nutritional preparation sufficiency before CD operations. Preoperative treatment with the aim of reducing CRP level and improving the patient's nutritional status may be helpful to reduce the rate of PICs.