The paper discusses the effect of profit quality from main operating profit by an analyses on the relationships proportion of main operating profit and ratio of net earning to net asset , Empirical evidence indicates there is reverse relationship between main operating profit and the variance coefficient of ratio of net earning to net asset, but positive relationship between the variance coefficient of proportion of main operating profit and the variance coefficient of ratio of net earning to net asset. Studies prove that the stability and durability mostly depend the proportion of main operating profit in gross profit. So listed companies should attach importance to main operating profit and improve the proportion of main operating profit in gross profit.