For relieving the damage from the Phyllocnistis citrella, the relationship between the first appearance of the Phyllocnistis citrella and the background of weather and climate conditions was discussed and a forecast system utilizing the observation of meteorological elements was modeled in this study. The atmospheric circulation, surface weather system and the low-level jet during the period of Phyllocnistis citrella first appearance were analyzed by using the NCEP/NCAR reanalysis data and the historical data of the weather information comprehensive processing system MICAPS. The first appearance of the Phyllocnistis citrella could be classified into two categories: the early period, the Phyllocnistis citrella first appearance in May or June, and the later period while in July to September. It was found that: the average atmospheric circulation and the average temperature field were quite different between the early period and the later period; if the ground low-pressure had last several days, it was mostly that the Phyllocnistis citrella would appear in Quzhou during the first period and the appearance of Phyllocnistis citrella in later period was directly related to the landing typhoon which first occurred in Zhejiang or north of Fujian. The southwest or east lower jet always occured in south China or the east coast and maintains more than two days before the appearance of Phyllocnistis citrella. The result showed positive correlation between the cumulative temperature, precipitation, relative humidity and vapour pressure and the first appearance of the Phyllocnistis citrella in the early period. The forecasting model of the appearance of the Phyllocnistis citrella and the index of 5-day rolling forecast were built by the observation of meteorological elements.