Agricultural drainage water sampling was conducted along ditch systems from 1st order to 5th order in Nongjiang River and Bielahonghe River during June to September, 2005. The spatio-temporal dynamics of nitrogen concentrations in agricultural ditch systems were analyzed. Results showed that there were higher concentrations of nitrogen in Bielahonghe ditch system. Peak values of TN, NH4(+) -N and NO3(-) -N moved from 1" order to 3rd and 5th order in Nongjiang and Bielahonghe ditch systems respectively. The retention of nitrogen in Bielahonghe ditch system was more than Nongjiang ditch system. The temporal dynamics of TN and NH4(+) -N were parallel in the two ditch systems, which decreased from June to September. But the temporal dynamics of NO3(-) -N had no obvious trend. The relationships between TN and NH4(+) -N and NO3(-) -N were positively correlated in both Nongjiang and Bielahonghe ditch systems, fitting for Power model and Cubic model respectively. The relationships between TN and NH4(+) -N and NO3(-) -N can be described by multi-variance linear regression, which explained 78% of TN concentration in Bielahonghe ditch system.