Objective To evaluate MRI in judging the therapeutic effect of argon-helium cryoablation therapy for prostate cancer. Methods The clinical data and imaging materials of 16 patients with prostate cancer , who had received ultrasound-guided argon-helium knife cryogenic treatment at authors ’ hospital during the period from March 2012 to Oct. 2014, were retrospectively and comprehensively analyzed. The preoperative and postoperative laboratory test results were compared with MRI findings, and the ablation effect was assessed, focusing on the surgical residue, metastasis, etc. Results One months after the surgery, MRI demonstrated that satisfactory ablation extent was obtained in all patients, the ablated tumor tissue was characterized by long-T2 signal and no obvious recurrence could be found on DWI and DCE-MRI. A slight decrease of PSA level was observed. Six months after the surgery, MRI revealed that the prostate size was significantly reduced, PSA level was markedly decreased and no obvious evidence of recurrence was observed. No severe postoperative complications, such as urethral necrosis, urethral stricture or urethro-rectal fistula, occurred. During the 6-month following-up time, one patient died from other causes. Conclusion MRI has excellent clinical application value in estimating the ablation extent and in judging postoperative recurrence or metastasis of prostate cancer after argon-helium cryoablation treatment.