Abstract: The biological characters of Psylla chinesis Yang et Li were studied systematically from 1987 to 1991. The results are as follows: (1) There are 6-7 generations a year on pear trees in the centre and south of Hebei Province. The peak of emergence occurrs from June to July. The period and stadium of every metamorphosises and generations was discovered. (2) The nymph of Psylla chinesis begin to release mucus in 3~7 days and it would be covered by mucus in 4~20 days. The mucus is a complex mixture of high molecular organic substances which contain =GH2, -OH, -NH2, C-H and C-O groups. (3) The spatial distribution patterns of the nymph in crowns and orchards are all determined as aggregate-type.(4) The lowest number of adult female suckers which cause the leaves fall are 4 on a leaf base and 12 on a leaf blade. (5) The place where the adults overwinter is in the fallen leaves and withered grasses. The results provided scientific basis for effective control.