The invention discloses a temperature- and humidity-based method for calculating ammonia emission quantity of a nationwide large-scale livestock farm. The method comprises the following steps of (a) acquiring nationwide temperature and humidity data within a year, and dividing the data into a plurality of temperature and humidity segments; (b) selecting a plurality of large-scale livestock farms from each temperature and humidity segment within a national range as measurement points; (c) performing field investigation on each measurement point, and determining types and numbers of livestock cultured at each measurement point; (d) observing and collecting unit livestock ammonia emission rate and corresponding temperature and humidity information of each measurement point; and (e) summarizing the livestock types and numbers which are collected by the plurality of measurement points arranged at different temperature and humidity segments, the unit livestock ammonia emission rate and the corresponding temperature and humidity information, and respectively fitting unit livestock ammonia emission rates of different temperature and humidity segments and temperature and humidity integral response relations according to the characteristic that the livestock ammonia emission is extremely affected by temperature and humidity.