The red imported fire ant, Solenopsis invicta, is a global invasive insect pest. Currently, chemical treatment is the primary method for fire ant control. However, most chemicals are unsuitable for environmentally sensitive areas, such as urban green spaces and organic farms. Ammonia is the simplest pnictogen hydride and is more ecologically friendly in urban green spaces. To screen green non-chemical control agents for S. invicta that can be used in urban green spaces, the efficacy of ammonia against red imported fire ants was evaluated in combination with indoor and field trials. In this paper, the toxicity of ammonia on workers and alates of S. invicta was tested under laboratory conditions. After 24 h treatment with 15.81 mg/L ammonia, the mortality of workers, males, and female alates were 100%, 87.07%, and 97.41%, respectively. After 24 h treatment with 17.56 mg/L ammonia, the mortality of both male and female alates is over 99.14%. In addition, the tolerance of alates to ammonia fumigation was much higher than workers. The field trials showed that the mortality of fire ant mounds and reduction rate of workers were 60.83% and 54.36% after 14 d mound drench of 24.59 g/L ammonia treatment, respectively. This study provides a critical, necessary, essential, vital, and theoretical basis for the use of ammonia for the control of crucial theoretical basis for the use of ammonia to control S. invicta in urban greenfield habitats.