Abstract: This paper described the working principle,structure,function and features of NGAM- 2008 natural gamma ray ash monitor,and evaluated the application situation and result in coal preparation plant of Dongtan coal mine. The comparison test and application result show that the ash monitor is satisfied the user’s requirement,operation result is better,small workload in maintenance,without using radioactive source,safety and reliable,that significantly reduced the managing coat. Finally described the matters should attention in routine maintenance service.