Colorectal cancer (CRC) is one of the most frequent cancers around the world. Multimodality therapies are used for CRC including surgery, chemotherapy, radiotherapy and targeted therapy. Correct treatment plan depends greatly on the accurate pretreatment staging. Computed tomography (CT) is a widely used detection and staging modality for CRC patients in clinical practice. The role of CT in assessing the patients with CRC has been well established, but the accuracy of pretreatment staging by CT varies in different reports. With the development of CT techniques, some reformations such as multi-detector CT (MDCT), CT with water enema or air insufflations, multiple planner reconstruction (MPR) help to give us higher resolution images in shorter time. The accuracy of CT for N staging was still not so ideal, but CT played an important role in chest and liver staging. Magnetic resonance imaging (MRI) and endorectal ultrasound (ERUS) may provide more precise images and evaluation of local T and N staging for rectal cancer. And positron emission tomography (PET) or PET/CT is recommended as a complement of CT, only for cases suspected of residual or recurrent colorectal carcinoma or before metastasectomy, not for routine use.