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In this research and according to level set method, 3D complex grains burn-back analysis is numerically simulated. The complicated grains that we have considered in this research, are included four types of difficulties that are insulated regions, different burning rates, non-uniform burning rates and oriented burning rates. To this end, the classical algorithm that is developed by authors, will be improved for simulation of above mentioned grains. In the first step, and for simulation of insulated grains, linear, quadratic, and combined insulators are considered. In the next step, the simulation of grains with different burning rates in desired directions, are added to the main program. Finally, by considering non uniform burning rate in axial and/or radial directions, improvement of the code is completed. Comparison of results in cylindrical grains according to present and analytical methods, indicate that the present algorithm is capable for simulation of complicated grains. Also, some complex grains that we can not simulate them analytically or based on the classical level set method, are considered and evaluated.