Abstract: Field measurements relating to acid rain were made in spring 1993 along Hunan Section,Jingguang Railroad.The pollution status,characteristics,sources and formation mechanism of acid precipitation were also studied and discussed.The results show that precipitation in spring in Hunan region is serious polluted acid rain with sulfuric acid;its formation mechanism is basically the same as that in South China;the concentrations of pollutants result from the contribution of both local sourecs and transport of external sources.