The natural dynamics of the population density and mound density of imported fire ants Solenopsis invicta Buren has been studied from April 2009 to March 2010 in Shenzhen City. The results were as follows: the population density of workers appeared in curve with multiple peaks, the primary peak during late April to early July, the second peak during early September to late October, and the rest during mid February to late March in order. The mound density began to increase in late February, with the peak during early May to late August, and it started to decrease in early September until the bottom in mid February of the next year; afterwards, it began to rise in late February. New mounds appeared respectively during April to July, in November and in February and March of the following year, with the highest density in mid April. The disappearance of the mounds occurred throughout the year, except in May, June, August and next February, March, and the highest number of mound disappearance occurred in early September. The population density and surface temperature, active mound density and ten day average temperature there have a positive correlation.