In order to make tree management more efficient, it is necessary to make conventional visual diagnosis objective. The NDVI can be calculated by using near-infrared images, and that NDVI is likely to objectively show the decline diagnosis for trees diagnosis that changes depending on the subjectivity. Near-infrared images were acquired by taking image from the ground, and taken from the air using UAV. The near-infrared image was imported into ArcGIS, and the NDVI image was calculated. Arbitrary 15 points were created at the leaves of the tree and numerical information was extracted. The degree of decline has an integer value of 0 to 4, and a larger value indicates a decline. NDVI is an index indicating the vegetation activity, and has a range of 1 to -1 and the closer to 1, the higher the activity. Therefore, correlation analysis process confirms that NDVI is correlated with the decline diagnosis visually assessed on the ground. As a result, NDVI decreases when the degree of decline is high and increases when the degree of decline is low. The correlation coefficient between ground NDVI and decline was -0.769, and the correlation coefficient between airborne NDVI and decline was -0.678. Both results were confirmed to be statistically significant negative correlations. In the future, as the accuracy improves, it can be used as an indicator to understand the condition of trees in the decline diagnosis.