【Background】The cotton mealybug Phenacoccus solenopsis Tinsley is a new cotton pest worldwide. The mealybug was found in August 2008 in Guangzhou, and could seriously threaten the cotton production in China. 【Method】The invasion and colonization for the mealybug populations in cotton and tomato fields in Guangzhou was investigated by methods of releasing the 1st instar nymph and following in a systematic survey. 【Result】The results revealed that the initial population declined sharply within 3 days after release, with a mortality of 82.[KG-*8]7% and 61.[KG-*8]2% in cotton and tomato fields, respectively. After developed into 3rd nymph, the population decline became slow. The probabilities which females reached oviposition were 2.[KG-*8]83% and 2.[KG-*8]5% in cotton and tomato fields, respectively. The fecundities of the adult females in cotton and tomato fields were 532.[KG-*8]6 individuals and 418.[KG-*8]4 individuals/female, respectively, and population trend indices were 15.[KG-*8]1and 10.[KG-*8]5 on the two host crops. The survival curves for the mealybug populations in cotton and tomato fields were fitted to type Ι, and the relationship between survival rate and the duration could be described with the models S=(1.[KG-*8]0000+1.[KG-*8]1505D)-1.[KG-*8]1250 on cotton, and S=(0.[KG-*8]9996+0.[KG-*8]12481D)-3.[KG-*8]0614 on tomato. The minimum invasive population producing at least one ovipositing female for P.solenopsis mealybug ranged from 36 to 40 individuals according to the probabilities from 1st nymph to adult female in oviposition period. 【Conclusion and significance】The survival curve of P.solenopsis invading tomato and cotton in June~August in Guangzhou was Ι type (concave), the minimum level for invasive population is 36~40 individuals.