Objective To establish an immunocompetent pancreatic cancer bearing mice model and clarify the dynamic changes of the CD11b+ GR-1 + myeloid derived suppressor cells (MDSC),CD11 b + Ly6Clow Ly6G + polymorphonuclear myeloid derived suppressor cells (PMN-MDSC) and CD1 1b + Ly6C + Ly6G-monocytic myeloid derived suppressor cells (Mo-MDSC),F4/80+ tumor associated macrophages (TAM) and F4/80 + CD16/32 + CD206-classical activated macrophages (M1),F4/80 + CD16/32-CD206 + adaptive activated macrophages (M2) in pancreatic cancer bearing mice.Methods The C57B6/J mice syngeneic pancreatic adenocarcinoma cell line Panc02 ceils were subcutaneously implanted to establish the immunocompetent murine pancreatic cancer bearing model.According to the tumor size,it was divided into four stages,named T1-T4.The flow cytometry (FCM) was performed to identify the different cell populations.Results With tumor progression,the MDSC population was consistently increased [for peripheral blood,T1 vs.T4,(4.95 ±1.03)％ vs.(36.45 ±6.43)％,P＜0.01; for tumor tissue,T1 vs.T4,(2.95 ± 2.95) ％ vs.(18.17 ± 3.30) ％,P ＜ 0.01],and the PMN-MDSC was the main subpopulation and dramatically increased [for peripheral blood,T1 vs.T4,(29.73 ± 10.30) ％ vs.(66.40 ± 12.10)％,P＜0.01; for tumor tissue,T1 vs.T4,(24.73±10.81)％ vs.(73.17±10.81)％,P＜ 0.01],but the other subtype Mo-MDSC did not significantly change [for peripheral blood,T1 vs.T4,(10.30 ± 1.90) ％ vs.(9.87 ± 1.91) ％,P ＞ 0.05 ; for tumor tissue,T1 vs.T4,(9.10 ± 1.01) ％ vs.(9.90 ±2.21)％,P ＞0.05].The TAM in peripheral blood in T1-T3 stages was consistently increased,including both M1 and M2 [for M1,T1 vs.T3,(6.30 ± 1.25) ％ vs.(20.17 ±2.31) ％,P ＜0.01 ; for M2,(0.87 ± 0.21) ％ vs.(5.40 ± 0.85) ％,P ＜ 0.01],but the M2/M1 ratio became bigger.The peripheral blood macrophages in T4 stage were dramatically declined [T3 vs.T4,(20.17 ± 2.31) ％ vs.(10.77 ± 1.52) ％,P ＜0.01],but M2 was still increased [T3 vs.T4,(6.80 ± 0.75) ％ vs.(8.97 ± 1.20)％,P ＜0.05].The intratumoral M2 tumor associated macrophages were consistently increased [T1 vs.T4,(2.94 ±0.51)％ vs.(13.44 ±2.95)％,P＜0.01],but the M1 did not significantly change [T1 vs.T4,(6.49 ± 1.39) ％ vs.(7.26 ± 1.96) ％,P ＞ 0.05].The ratio of M2/M1 was bigger than that of peripheral blood at the same stage.Conclusion The PMN-MDSC × M2/M1 ratio in peripheral blood and tumor tissue is the formidable surrogate for the tumor burden of pancreatic cancer bearing mice and can be used as a predictor for the prognosis of patients with pancreatic cancer.