The malignant transformation of astrocytoma may result from the accumulation of multiple genetic alterations. Current research shows that diffuse astrocytoma (AIIs, WHO grade II) is inherently predisposed to recur locally, and to spontaneously progress to anaplastic astrocytoma (AAIIIs, WHO grade III) and eventually secondary glioblastoma (sGBMIVs, WHO grade IV). The aim of the study was to identify and validate the important gene(s) associated with malignant progression and poor prognosis of astrocytoma. Average expression levels of 82 samples (35 AIIs, 13 AAIIIs and 34 sGBMIVs) were compared to each other through no-paired student test. Candidate genes were screened by DAVID and Kaplan-Meier survival analysis. Further, the significant candidate genes were validated through real-time PCR(qPCR), western blot and immunohistochemistry (IHC) in different grades of glioma. Finally, the association of target gene and clinical molecular characterization was analyzed by Chi-squared analysis. The cell-division cycle protein 20(CDC20, p = 0.0129) and the polo-like kinase 1(PLK1, p = 0.0046) were screened by statistical and Kaplan-Meier survival analysis. The expression levels of CDC20 and PLK1 rose significantly through real-time PCR(qPCR), western blot and IHC. A chi-squared analysis showed that patients with CDC20 high-expression differ from patients with CDC20 low-expression in terms of WHO classification (p < 0.0001), karnofsky performance score (KPS, p < 0.0001), isocitrate dehydrogenase mutation (IDH1, p < 0.0001), phosphatase and tensin homolog mutation (PTEN, p = 0.027) and epidermal growth factor receptor protein amplification (EGFR, p = 0.048). Moreover, the biological processes analyses indicate CDC20 might have an essential role in astrocyte cell proliferation. We demonstrated that the expression level of CDC20 increases significantly along with malignant progression and poor prognosis of astrocytoma.