Abstract: The harm characteristics and population dynamics of Holcocerus hippophaecolus eggs and larvae were investigated from May to November, 2003 in Jianping County, northeast China. The eggs of seabuckthorn carpenterworm are largely distributed in the crevices and wounds of the stem of host trees. The newly-hatched larvae first harm the phloem of the stem and then transfers from the stem to the root. The larvae under the ground mainly damage the xylem and transfers between the taproots and the lateral roots. The eggs and larvae mostly aggregate below the 2 m height of the stem and the larvae in the roots aggregate within 20 cm of taproots under ground. From May to November, the larvae hatched in past years descended, especially in June and October. Then the larvae hatched in the new-year increased gradually from July and culminated in September, but decreased sharply later. From August to November, both aggregation location and population quantity of the larvae transferred from the stem to the root. In early October, 70.5% of larvae distributed in the root, and only about 29.5% in the stem, mainly aggregating below 1.2 m of the stem. In November, almost all larvae stayed in the root, seldom in the stem.