To perceive long-term leaf area index, foliage clumping index and canopy density index data of forest canopy structure parameters, an automatic instrument was designed. With this instrument, an effective solution was provided to obtain canopy structural parameter for forest management plan and to collect long-term data for scientific research. The instrument was made up of measuring vehicle, designed orbit and solar energy system. The measuring vehicle was controlled by single chip microcomputer to complete the assigned tasks, such as collecting intensity distribution data of orbital light and obtaining probability distribution function of light spots in different lengths. A large flare elimination method and Bell's Law were used to calculate the forest canopy structure parameters. Leaf area index was measured via a non-destructive optical method, which was applied to crown canopy leaf area index long-term measurement, and then gain the long time serial data. The leaves of 32 plots of experimental forest were tested to measure the accuracy and solver of this method. Results showed that the effective leaf area index obtained via this instrument was similar to LAI-2200 measurement with correlation coefficient of 0.8325, and canopy density index was consistent with what traditional methods did.