Objective To explore the possible cytokine mechanism of delayed skin wound healing in mice exposed to ionizing radiation(IR), so as to provide evidence for further research. Methods Totally 68 female Kunming mice were randomly divided into two groups. Back skin defect was made in mice of the experimental group (n=34) immediately after exposure to 6 Gy^{60n=34) had skin defect but with no radiation exposure. Wound areas were continuously measured and wound healing rates were monitored on day 2, 4, 6, 8, 10, 12, and 14 after damage (n=10). Mice were sacrificed on day 1, 3, 5, and 7 (each time point 6 mice), the skin and thin layer of muscle tissues around the wound were obtained, and H E staining was used for evaluating wound healing. Platelet derived growth factor BB （PDGF-BB） and tumor necrosis factor alpha (TNF-α) expression levels in the dermal defects were examined by immunohistochemical methods and real time PCR. Results The wound healing rate in the experimental group was significantly lower than that in the control group within 14 days after damage(P<0.01). On day 14 the wound healing rate in the experimental group was significantly lower than that in the control group (61.61% and 90.13%, P<0.01). H E staining showed more severe inflammatory cell infiltration, disarranged collagen fibers and less proliferation of fibroblasts in the wound of experimental group compared with that of the control group. Immunohistochemical and real time PCR results demonstrated that PDGF BB expression in experimental group was significantly less than that in the control group from day 3 to day 7 (P<0.05). PDGF-BB gene expression in experimental group was less than that in the control group from day 3 (P<0.01). The expression of TNF α protein and gene was up regulated in both groups and reached the peak on day 5, then began to decrease. On day 7, TNF α protein and gene expression in the experimental group was significantly higher than that in the control group (P<0.01). Conclusion PDGF-BB and TNF-α participate in delayed wound healing in ionizing radiation mice with dermal defects.}