Long course radiotherapy plus neoadjuvant chemotherapy followed by resection total mesorecta excision has accepted widespread recognized in the treatment of locally advanced rectal cancer (LARC). Tislelizumab, an anti-PD1(programmed death 1) humanized IgG4 (Immunoglomin G4) monoclonal antibody, has been demonstrated with clinical activity and is approved for treating recurrent/refractory classical Hodgkin lymphoma and locally advanced/metastatic urothelial carcinoma in China. The aim of This NCRT-PD-1-LARC trial is to evaluate the efficacy and safety of long course neoadjuvant chemoradiotherapy plus tislelizumab followed by total mesorecta excision for LARC. This NCRT-PD-1-LARC trial will be a prospective, multicenter and phase Ⅱ clinical trial designed to evaluate the safety and efficacy of LARC patients treated with long course neoadjuvant chemoradiotherapy plus tislelizumab followed by total mesorecta excision. It will consecutively enroll 50 stage II/III LARC patients (cT3N0M0 and cT1-3N1-2M0) with the tumor distal location ≤ 10cm from anal verge at 7 centers in China. The enrolled patients will receive long course radiotherapy (50 Gy/25 f, 2 Gy/f, 5 days/week) and three 21-day cycles capecitabine (1000 mg/m2, bid, po, day1-14) plus three 21-day cycles tislelizumab (200 mg, iv.gtt, day8), followed by total mesorecta excision 6-12 week after the end of radiotherapy. The primary efficacy endpoint will be the pathological complete response (pCR) rate, which is defined as absence of viable tumor cells in the primary tumor and lymph nodes.