A method by controlling the primary aberration of each surface in the system based on Seidel aberration theory is proposed for reducing system tolerance sensitivity. First of all, it illustrates the principle of small aberrations balancing, and then the relation of the Seidel aberration theory and tolerance sensitivity is indicated by theoretical formula. At last, we enumerate an example which is the optical design of objective lens of aerial camera and make tolerances analysis both on the compensation of big aberration and small aberration. The results show looser tolerances distribution, better stability and great reduction of the cost on the compensation of small aberration.