The effect of quaternary red soil moisture on ammonia volatilization of urea was studied by greenhouse simulation. The results showed that there was no significant correlation between ammonia volatilization flux and soil moisture, but the peak of ammonia volatilization flux at the higher moisture treatments (280, 320 and 360 g/kg) appeared 10 days earlier than at the lower ones (160 and 200 g/kg). Ammonia volatilization of urea in red soil could be divided into two stages, namely, rapidly and slowly increasing stages. The relationship between the cumulative ammonia-volatilization flux (y) and the corresponding time (t) followed Elovich equation (y = a + blnt), y increased with soil moisture increased from the first day to the tenth day, then it decreased to the lowest (0.90 g, accounted for 9.0% for urea applied) when soil moisture was 240 g/kg. The highest y was 1.16 g and accounted for 11.6% for urea applied when soil moisture was 320 g/kg.