A new coupled model PCPF-1 and HYDRUS-2D had been developed. This new coupled model allows to simulate fate and behavior of pesticide in paddy water and paddy soil within one full agronomic crop season (from transplanting, after puddling, to harvest including mid term drainage). PCPF-1 is a lumped model, which is based on water and pesticide mass balance (Watanabe and Takagi, 2000a,b). It simulates the fate and behavior of pesticide in surface compartment (including paddy water and the first centimeter of paddy soil), by taking into account paddy water management. HYDRUS-2D is a popular numerical finite element model (Simunek et al, 1998). It solves Richard`s and advection-dispersion equations, including adsorption and degradation phenomena in the soil compartment. Longitudinal dispersivity, halflife and adsorption parameters were used to simulate pesticide transfer in soil. The coupling involved some improvements in exchanges of water and pollutant concentration at the soil interface between both compartments. The monitoring data collected from experimental plots in Tsukuba (NIAES) in 1998 and 1999 were used to calibrated hydraulic properties and functioning of paddy soil. It had been evaluated with tracer (KCl) experiment and thus with pesticide data (Mefenacet and Pretilachlor). The hydraulic functioning study confirmed that the hard pan layer is the key factor controlling percolation rate and pollutant dissipation. Matric potential and tracer monitoring highlighted evolution of hard pan layer properties (Ksat)slightly decreased during days after puddling by clay clogging and strongly increased after mid term drainage by drying cracks. The tracer and pesticide travel times in paddy soil are about 30 and 90 days after application at 15 cm and 45 cm depth respectively. The model allows to calculate residential time in every soil layers and to assess leaching below hard pan layer. It provides a good estimation of pesticide persistence after one full crop season.