The study evaluates the combination of immunotherapy of PD-1 antibody and chemotherapy and neoadjuvant short-course radiotherapy in locally advanced colon cancer (LACC). Patients are randomly assigned into two prospective groups: treatment group and observerment group. In treatment group, a total of 60 patients will receive 5*5Gy short-course radiotherapy, followed by 4 cycles of capecitabine plus oxaliplatin (CAPOX) chemotherapy and PD-1 antibody, finally receive the surgery. In observerment group: a total of 60 patients will receive 4 cycles of CAPOX chemotherapy, then receive the surgery. The rate of pathologic complete response （pCR）, long-term prognosis and adverse effects will be analyzed.

This study is a prospective, randomized controlled, multicenter phase II study, with a design of superior efficacy，to compare the efficacy of neoadjuvant short-course radiotherapy combined with CapOX chemotherapy and PD-1 immunotherapy in locally advanced colon cancer. We will consecutively enrolled patients who were diagnosed with locally advanced colon cancer with T4 stage or bulky nodes. A total of 120 patients will be Randomized 1:1 to the treatment group and observerment group. In observerment group, patients will receive 4 cycles of CAPOX (Capecitabine: 1000mg/m2 d1-14 q3w; Oxaliplatin: 130mg/m2 d1 q3w)chemotherapy, then receive the surgery, followed by 4 cycles of CAPOX. In treatment group, patients will receive 5*5Gy short-course radiotherapy, followed by 4 cycles of CAPOXand PD-1 antibody(Serplulimab,300mg d1 q3w), then receive the surgery,followed by 4 cycles of CAPOX.

Inclusion Criteria:

1. pathological confirmed adenocarcinoma
2. clinical stage T4 and/or bulky nodes
3. the distance from anal verge more than 15 cm
4. without distance metastases
5. age >=18 years old, female and male
6. KPS >=70
7. without previous anti-cancer therapy or immunotherapy
8. with good compliance
9. signed the inform consent

Exclusion Criteria:

1. pregnancy or breast-feeding women
2. history of other malignancies within 5 years
3. serious medical illness, such as severe mental disorders, cardiac disease, uncontrolled infection, etc.
4. immunodeficiency disease or long-term using of immunosuppressive agents
5. baseline blood and biochemical indicators do not meet the following criteria: neutrophils≥1.5×10^9/L, Hb≥90g/L, PLT≥100×10^9/L, ALT/AST ≤2.5 ULN, Cr≤ 1 ULN
6. allergic to any component of the therapy