Abstract: Climate change is currently a global concern, which is mainly caused by excessive emission of greenhouse gases to the atmosphere, in particular the emission of CH4, N2O and CO2 from agricultural production process. Greenhouse gas produced from manure management in livestock and poultry production is an important source of greenhouse gas emission. Besides, fermentation process of animal manure may generate large amount of NH3, which is considered as an important contaminant gas to the environmental and ecological system. Among agricultural sector, dairy farm is a big source of greenhouse gas and NH3 emission. In China, a barn with a fully open lot, where the cows are freely accessible, is a typical operation for dairy cattle. Manure on the surface of the open lots is typically removed from days to weeks depending the climate and management in the farms, while the remained manure, liquid penetration and the cows on the lot are important sources of contaminated gas emissions. However, there are few field studies on the emissions from the lot because of its open characterization, relative low gas concentration and the potential impact on the daily management of the farms. In this paper, an integrated horizontal flux method, based on the mass balance principle, was used to calculate the emission fluxes of CH4, N2O, CO2 and NH3 from a typical dairy open lot in Beijing in spring season by continuous measurement of their concentrations with the purpose to provide fundamental information on the emissions. As the emission source, the open lot, which was 40 m in length by 27 m in width and kept with 52 milking cows, was divided into upwind boundary and downwind boundary according to the dominating wind directions. The emission rate was calculated based on the concentration differences of the target gases continuously measured from the upwind and downwind boundaries at three different heights of 1, 2 and 3 m by a photoacoustic field gas-monitor (INNOVA 1412i) and self-developed multiplexer. The results showed the overall emission rates of CH4, N2O, CO2 and NH3 from the dairy open lot were 155.59, 3.60, 4 869.37 and 66.27 mg/(m2·h) during the field measurement, respectively. The emissions of all the gases reached their daily peaks after manure removal in late afternoon. The emissions of CH4, N2O and CO2(based on CO2 equivalents) of the open lot accounted for 42.79%, 9.37% and 47.83% of the total greenhouse gases emissions, respectively; and their proportions were related to the climate, manure management strategies of the lot, and feed in gredients as well. Additionally, CH4, N2O and NH3 emission rates were significantly and positively affected by ambient temperature (P<0.05). CH4, N2O and NH3 emission rates could also be enhanced by wind speed within some limits. When the surface wind speed was around 5.16 m/s, which was measured on the point 1 m above the ground, the emissions of the three gases were significantly differed from those under 4.05 and 4.75 m/s (P<0.05). While, when the wind speed was at 18.85 m/s, the emission rates were decreased, which could be explained by the crust formed on the manure surface due to the drying process under much higher wind speed and its prevention on the emissions. Besides, manure removal activity increased the emissions of gases, and the impacts of ambient temperature and wind speed on the gas emission may also be altered to some extent.