Ammonia (NH₃) is formed constantly in soils because of the biological degradation of organic compounds and NH₄⁺ yielding mineral and organic fertilizers.NH₃ volatilization is one of the major losses of applied nitrogen fertilizers, which is affected by the local climate conditions (e.g., temperature, sun illumination, and wind speed), soil moisture content, urease activity,fertilization time, and ammonium concentration in surface water of the paddy fields. In this study, A situ experiment combined with venting method was conducted to study the effects of different fertilization patterns on NH₃ volatilization in Chao Lake Basin during the rice season in 2010. In the experiment,there were six treatments with the control,the conventional fertilization, the optimization fertilization(according to local test of fertilization recipe ), the reduction by 30% of nitrogen fertilizer,the reduction by 50% of phosphorus fertilizer and the straw return.The results showed that the NH₃ volatilization loss from paddy fields was affected by fertilization and ammonium nitrogen(NH₄⁺-N )concentration in surface water of the paddy fields.The NH₃ volatilization among different treatments lasted for one week and the volatilization peak occurred within one to three days after fertilization,then declined quickly.When the rate of phosphorus fertilizer remained the same(e.g.,he treatments of the optimization fertilization and the reduction by 30% of nitrogen fertilizer ),The concentration of NH₃ volatilization loss enhanced as the nitrogen application rate increased with the same rate of phosphorus fertilizer. The amount of NH₃ volatilization ranged from 7.22 to 14.20 kg/hm², Which accounted for 4.59% to 6.64% of the total applied N for the whole period of rice growth. Compared with the conventional fertilization, the NH₃ volatilization loss was reduced by 1% to 2% respectively with the treatments of the reduction by 30% of nitrogen fertilizer、by 50% of phosphorus fertilizer and the optimization fertilization, while the NH₃ volatilization loss was reduced by 6.98 kg/hm² with the treatment of the straw return,which total ammonia volatilize quantity was 54% of the conventional fertilization.The highest NH₃ volatilization loss occurred at basal dressing,which amount for 60% of the total NH₃ loss, while the lowest loss did at panicle stage. The concentration of NH₄⁺-N in surface water reached the highest within one to two days after fertilization.The positive correlation was observed between NH₃ loss and NH₄⁺-N concentration in the surface water of the basal dressing and the first top-dressing.From the point of the water improvement of Chao Lake basin,the period within a week after the fertilizer application was a critical time to control N loss and leaching from flooded paddy fields. NH₃ loss would be decreased when N and P ferlization was rational. It is necessary to apply rational and balanced fertilization for N and P. Combined with economic benefit and environmental risk,the straw return is recommended for rice production in Chao Lake basin.