Objective To explore the value of apparent diffusion coefficient(ADC)values of magnetic resonance diffusion weighted imaging(MR-DWI)in predicting the prognosis of primary hepatocellular carcinoma(HCC)treated by radiofrequency ablation(RFA).Methods A prospective study was conducted on 178 patients with HCC.All patients were treated with RFA and followed up for 1 year after treatment.MR-DWI was performed before RFA and one month after RFA,and the changes in ADC value were calculated.These changes of the cancer in patients with different clinicopathological parameters were compared.The factors affecting the prognosis of HCC patients with RFA,and the value of ADC value changes in predicting the prognosis were analyzed.Results The changes of ADC values in patients with high alpha-fetoprotein,Barcelona clinic live cancer(BCLC)stage C,and poorly differentiated were lower than those in patients with low alpha-fetoprotein,BCLC stage B,and moderately well-differentiated(P<0.05).Six cases were lost to follow-up,and 120 of the remaining 172 patients survived.Cox regression analysis showed that the changes in ADC value,tumor stage and degree of differentiation were independent factors affecting the prognosis of HCC patients with RFA(P<0.05).Receiver operating characteristic(ROC)curve results showed that the best cut-off point,sensitivity,specificity and area under the curve(AUC)of ADC value change in predicting the prognosis of HCC patients with RFA were 0.42×10-3 mm2/s,75.00%,78.33%and 0.801.There were 16 deaths in the high change group of ADC value(>0.42)and 36 deaths in the low change group(≤0.42).The overall survival curve of the high change group of ADC value was better than that of the low change group(P<0.05).Conclusion The change in ADC value of MR-DWI sequence before and after short-term RFA treatment in HCC patients is related to the patient's pathology and prognosis,with a good predictive effect.The low change in ADC value has a higher risk of poor prognosis.