Straw returning to the field has the regulation effect for ammonia emission pollution in agricultural surface source. Monitoring regional volatilization concentration to accurately obtain the ammonia dynamic characteristics is the precondition for emission rule studying. The infrared absorption spectral characteristics of ammonia were studied. Moreover, the quantitative inversion algorithm model was established, especially the correlation analysis and temperature correction function were optimized. The ammonia volatilization experiment was carried out in the demonstration area in Guoyang, Anhui in 2015 by the ammonia regional monitoring system based on open-path Tunable Diode Laser Absorption Spectroscopy(OPTDL). Then, ammonia dynamic volatilization character of corn and wheat straw returning to the field was studied. The monitoring results show that the ammonia concentration has a certain diurnal variation trend: it increased during the daytime and got to the maximum value at midday, then reduced gradually at night to the minimum. The typical hourly concentration varied from 0.6 10-3 to 1.34 10-3mmol/mol in summer, and it varied from 1.14 10-3 to 1.82 10-3mmol/mol in autumn. In autumn, the maximum daily average of ammonia volatilization from corn straw returning was 4.6 10-4mmol/mol, and it was 1.7 10-3mmol/mol from wheat straw returning in summer. The results indicate that the emission concentration rises significantly after more than one month of straw returning which has some certain seasonal difference in farmland scale. This infrared spectroscopy technology provides technical support for clarifying the ammonia emission rules in soil environment.