Colorectal cancer is one of the most common tumors in Asia. According to the recent research, surgical procedure could provide more treatment benefit in rectal cancer. Therefore, it was consider that important to standardized and improved the surgical procedure for rectal cancer. With the development of anatomical technique, minimally surgery with laparoscopy had become the trend for surgical treatment. There were several studies has been done to evaluate the safety and feasibility of laparoscopic surgery. In order to achieve better surgical outcome and reduce operative complications, the investigators design stratified randomization, double blinded, muti - center clinical trail to investigate the value of left colic artery in laparoscopic radical rectectomy.

Inclusion Criteria:

• Aged more then 18 years old;
• Diagnosed as rectal cancer with colonoscopic biopsy;
• Without metastasis;
• No Invasion of surrounding tissues;
• Limited operation;
• Underwent laparoscopic radical proctectomy(L-Dixon);
• BMI 18~30kg/m2;
• Without multiple primary tumors;
• Sign on the Medical informed Consent.

Exclusion Criteria:

• Simultaneous or simultaneous multiple primary colorectal cancer;
• Preoperative imaging examination results show: (1) Tumor involves the surrounding organs and combined organ resection need to be done; (2)distant metastasis; (3)unable to perform R0 resection;
• History of any other malignant tumor in recent 5 years;
• Patients need emergency operation;
• Not suitable for laparoscopic surgery;
• Women during Pregnancy or breast feeding period;
• Informed consent refusal