Abstract: This paper introduces the concept of subinjective dimension and obtains the nature of subinjective modules.Moreover subsemisimple ring,noether ring and hereditary ring are characteristiced.The main results are:(ⅰ)Any left R-module M is subinjective module if and only if SIdRM=0.(ⅱ)A ring R is subsemisimple ring if and only if SID(R)=0.(ⅲ)A ring R is Noether if and only if every subinjective module is injective.

Key words: subinjective modules, subinjective dimension；subsemisimple rings, noether rings, hereditary rings