Abstract: In order to establish monitoring method for ammonia emission in livestock enclosures and provide technical support for accurate calculation of ammonia emission in livestock enclosures, the natural ventilation pens of typical large-scale pig farms in Yangtze River Delta were taken as research object, and the influence of sampling efficiency, time and frequencies based on the ammonia monitoring standard method were discussed. The results show that the sampling efficiency was greater than 90% when the sampling time was more than 4 minutes (4 L collected gas) by the salicylic acid method, and there was no significant difference in the content of ammonia obtained by different sampling times (4, 20, 40 and 60 min). The relative error of hourly sampling frequency and 90% of cumulative frequency increased with the decrease of sampling frequency. The relative error in summer (with average daily temperature of 25-35℃) is significantly higher than that in winter (with average daily temperature of 0-10℃). Similar to the hourly sampling frequency, the average relative error of daily sampling frequency increased with the decrease of sampling frequency. In order to carry out ammonia monitoring in large-scale pig farms in the Yangtze River Delta, it is suggested that the sampling frequency should be no less than 4 times·h^-1 and increase to 6 times·h^-1 at 6-7 o'clock and in the afternoon in summer, and the daily sampling frequency should be no less than 12 times·d^-1 as well. While in winter, the sampling frequency should be 2 times·h^-1 and no less than 4 times·d^-1.