The CRC tissue of 27 patients with 5-FU chemotherapy-sensitive colorectal cancer （5-FU/S group） and 23 patients with 5-FU chemotherapy-resistant colorectal cancer （5-FU/R group） were collected. The expression levels of miR-30a-5p and TRIM31 mRNA in CRC tissue of the patients were detected by Real-time fluorescence quantitative PCR（RT-qPCR） method； the correlation between miR-30a-5p and TRIM31 mRNA expressions was analyzed by Pearson correlation analysis.The human CRC 5-FU resistant cells HT-29/5-FU cells and its parent HT-29 cells were cultured in vitro. The proliferation activities of two kinds of cells were detected by MTT assay， and the median inhibitory concentration （IC₅₀） and drug resistance index （RI） were calculated； the expression levels of miR-30a-5p and TRIM31 mRNA in two kinds of cells were detected by RT-qPCR method；the expression levels of TRIM31 protein in two kinds of cells were detected by Western blotting method. The HT-29/5-FU cells were further divided into blank control group， mimics NC group， miR-30a-5p mimics group， miR-30a-5p mimics+vector group and miR-30a-5p mimics+TRIM31 group. The cells in blank control group were not transfected， the cells in miR-30a-5p mimics group were transfected with miR-30a-5p mimics， the cells in miR-30a-5p mimics+vector group were transfected with miR-30a-5p mimics and negative control of vector， and the cells in miR-30a-5p mimics+TRIM31 group were transfected with miR-30a-5p mimics and TRIM31 over-expression vector. The expression levels of miR-30a-5p and TRIM31 mRNA in the HT-29/5-FU cells in various groups were detected by RT-qPCR method； the expression levels of TRIM31 protein in the HT-29/5-FU cells in various groups were detected by Western blotting method； the proliferation activities of the HT-29/5-FU cells in various groups were detected by MTT method； the apoptotic rates of the HT-29/5-FU cells in various groups were detected by flow cytometry；the targeted relationship between miR-30a-5p and TRIM31 was verified by dual-luciferase reporter gene system.

Compared with 5-FU/S group， the expression level of miR-30a-5p in cancer tissue of the patients in 5-FU/R group was decreased （P<0.01），and the expression level of TRIM31 mRNA was increased （P<0.01）. The expression levels of miR-30a-5p and TRIM31 mRNA were negatively correlated （R²=0.885，P<0.01）. Compared with HT-29 cells， the expression level of miR-30a-5p in the HT-29/5-FU cells was decreased （P<0.01），and the expression levels of TRIM31 mRNA and protein were increased （P<0.01）. The IC₅₀ values of HT-29/5-FU and HT-29 cells were （104.41±0.22） and （9.82±0.31） mg·L^－1， respectively， and the RI value was 12.42. Compared with blank control group or mimics NC group， the expression level of miR-30a-5p in the HT-29/5-FU cells in miR-30a-5p mimics group was increased （P<0.01）， the expression level of TRIM31 protein was decreased （P<0.01）， the proliferation activity of HT-29/5-FU cells was significantly decreased （P<0.01），and the apoptotic rate of HT-29/5-FU cells was significantly increased （P<0.01）. Compared with miR-30a-5p mimics group， the expression level of TRIM31 protein in the HT-29/5-FU cells in imiR-30a-5p mimics+TRIM31 group was increased （P<0.01）， the proliferation activity of HT-29/5-FU cells was significantly increased （P<0.01），and the apoptotic rate of HT-29/5-FU cells was significantly decreased （P<0.01）.The dual-luciferase reporter system results confirmed that TRIM31 was the target gene of miR -30a-5p.

Over-expression of miR-30a-5p enhances the sensitivity of the CRC drug-resistance cells to 5-FU by targeting the TRIM31 gene expression.