The characteristics of tropical cyclone (TC) over the western North Pac ific (WNP) in 2008 were reviewed, and its causation was analyzed. The results sh owed that the number of TC was less than the mean, the formative location was more concentrated and further west; the landing number was more than the normal, the first landed earlier, the landing position of TC was further south and landing time was more focused. The analyses of the main factors resulting in these anomalies showed that compared with means, the characteristics of the subtropical high were abnormal during the period of TC activity, including its area, strength, ridge position etc. which were unfavorable to the genesis and development of TC. And the anomaly distribution of important factors, such as the monsoon trough, vertical wind shear, sea surface temperature and OLR, was not favorable to the genesis of TC in the eastern WNP, which led to the decrease of TC number and the westward movement of genesis location.