Abstract: In 1997～1998,different doses of PWN were used to inoculate Pinus thunbergii and P. massoniana,3 origins of PWN were used to inoculate P.massoniana, 7 pine species were inoculated with PWN,and the oleoresin exudation of pines were observed at regular intervals. The results show that when the inoculum dose in less,the abnormal oleoresin exudation of pines appears later and abnormal. oleoresin exudation of all the tested pines needs longer time the abnormal oleoresin exudation of pines inoculated with PWN from Nanjing appears faster and abnormal oleoresin exudation of all the tested pines needs shorter time;the unusual oleoresin yields of all the tested pines for susceptible pine species manifest the fastest and almost all of the pines die,the unusual oleoresin yields of pines in middle susceptible display faster and part of pines die,the unusual oleoresin yields of resistant pines manifest the slowest and the abnormal oleoresin exudation class is low. In this test the abnormal oleoresin exudations of 98% pines inoculated with PWN occur. The results fully prove that oleoresin exudation method can be used as early diagnosis for pine wilt disease. Winter is the ideal season for felling infested pines.