The mining technique for natural gas hydrates is an essential technology to enable natural gas hydrates to replace conventional energy sources. This paper presents a steam mining system for natural gas hydrates (SMSGH) for exploiting natural gas hydrates in terrestrial permafrost regions. The system comprises of the surface steam heating device, underground mining, sealing device, surface gas collection, and ignition device. The working principle, design and calculation process, and structure composition of the system are described. The heating effect of the system is verified by laboratory experiments. The optimal heating parameters are proposed; steam open/closed pressure is 1.0/0.5 MPa. A field experiment was conducted in drilling wells of natural gas hydrates in Qilian Shan permafrost in Qinghai province, China. A total of 3.28 m(3) of natural gas was successfully exploited, and the ignition experiment was completed. This is the first study conducted in China that has successfully exploited natural gas hydrates in terrestrial permafrost.