The content of organic nitrogen(N) forms in soil profile were determined by using the method proposed by Bremner in 7 years protected field with different irrigation methods.The results indicated that the content of total N and organic N forms were decreased with layers' depth

but the ration of organic N forms to total N didn't had obvious rule.The difference of soil organic nitrogen forms was mainly in 0~50 cm soil layers under three irrigation methods

but below 50cm the difference was no obvious.At the same layer

acidic hydrolysable N was the main components of the organic N

the order of the content of acidic hydrolysable N forms and proportion to total N was unknown N > ammonia N > amino acid N > amino sugar N.At 0~80 cm soil layer

the proportion of acidic hydrolysable N to total N was mostly 58%~60%

but they were lower at 0~10cm and 10~20 cm of subsurface irrigation and 0~10 cm of furrow irrigation

the content respectively were 34.21%

50.75% and 48.02%.The proportion of non-acidic hydrolysable N to total N was 32%~36%.Compared with three irrigation methods

except for a few layers

the proportion of amino acid N

amino sugar N and ammonia N to total N in various layers of drip irrigation and subsurface irrigation were higher than furrow irrigation;but the proportion of unknown N and non-acidic hydrolysable N to total N of furrow irrigation were higher than drip irrigation and subsurface irrigation.