Abstract: In this paper, the theoretical analysis for the improvement of lateral mode selectivity and stability in sectional constricted planar composite cavity lasers (SCP) is made, and the effects of structural parameters on lateral mode selectivity and stability are numerically calculated. The calculated results indicate that, if the structural parameters and the ratio between CDH section and OS section cavity lengths are selected appropriately, the output power of the fundamental lateral mode in SCP lasers is more than 3-4 times that in ridge-guide CDH lasers.