Abstract: The stop of oleoresin exudation through trees is a major symptom of pine wood nematode disease. In Nanjing City,Japanese black pines and masson pines were inoculated with nematodes.Weakened trees were taken as a diagnosis standard. Results were shown: for Japanese black pine, accuracy was more than 93% after 12 days in the spring inoculation,80% after 20 days and 93% after 25 days in the summer inoculation. There was no obvious difference between 10～15 and 20～30 years old trees of the inoculated Japanese black pines. The amounts of oleoresin exudation of the masson pines inoculated with nematodes were obvious different with tree ages and inoculation periods. Bromophenol blue and dimethy yellow were used as indicators for early diagnosis, but the colour reactions were not distinct. Based on the test, early diagnosis of the trees in new disease area through observing the amounts of oleoresion exudation can be adopted to clean the disease trees thoroughly.