Abstract: The present paper deals with the work principle of a computer imaging identification system for the analysis of otolith microstructure of fish. With the system, identification and count of daily growth increments can be operated automatically, as well as measurement of the increment widths. In a few situations of incorrect identification, manual modification could be served as a correctional step. After identification and measurement, data of number such as daily growth increments and the increment widths in each sample were also automatically memorized in a file that can be read with Microsoft Excel. Examining of the system with lapillus of grass carp, Ctenopharyngodon idellus, had shown that all the daily growth increments in 28 of 30 samples were correctly identified and measured by computer, and only a few of the increments in the rest two samples were missed or falsely recorded. Manually, those missed or excrescent increments were added or deleted to the auto identified results. In other hand, with a 768?82 pixels BMP imaging file, the resolving power to the measurement of increment widths was 13 times higher than that measured manually with microscope alone.