Purpose To analyze the accuracy of MRI Diffusion-Weighted Imaging (DWI) in Gross Tumor Volume (GTV) delineation of esophageal squamous cell carcinoma (SCC).Methods and Materials Forty-two patients with esophageal SCC treated with radical surgery were analyzed.Routine CT scan, MRI T2-weighted and MRI DWI were employed before surgery; diffusion-sensitive gradient b-values were taken 400, 600 and 800s/mm2.GTV was delineated using CT, MRI T2-weighted images and DWI under different b-value images.The length of GTV measured under different images was compared with the pathological length and confirm the most accurate imaging modality,Use radiotherapy planning system to fuse DWI images and CT images to investigate the possibility of delineate GTV on fused images.Reslts The difference value of GTV length between CT, T2WI images and specimen was 3.63±12.06mm and 3.46±11.41mm.When b=400, 600 and 800s/mm2, the difference value between GTV length on the DWI images and on specimen was 0.73+6.09mm,-0.54±6.03mm and-1.58+5.71mm, respectively.the correlation coefficient of the measuring esophageal lengths on DWI images and the pathological lengths was 0.937, 0.940 and 0.944.DWI images and CT images could fuse accurately on radiotherapy planning system.GTV margin could show clearly on fused images.Conclusions DWI images can display the esophageal carcinoma lengths and margin accurately.When DWI images fused with CT images, GTV margin could show clearly, it can be used to delineate GTV accurately.