Objective To explore the impact of stress and inhibitor on avascular tumor growth. Methods A two-phase model, including the tumor cell and the extra-cellular interstitium is presented to describe avascular tumor growth. The diffusion of nutrients gives rise to the cellular growth while metabolism and inhibitor released by tumor cell itself accelerate the death rate. The continuum equation for tumor cell and the diffusion equation for nutrients and inhibitor are established. Given the interaction between the two phases, equations of momentum conservation are gained. With the constitutive relationship of each phase, the final coupled equations are linked together and numerical results are obtained. Results The tension of nutrients declines as time goes by, with lower value in the central area compared with its surrounding. Much more inhibitors are absorbed by the central area than its edge. Given the inhibitor and stress of each phase, the out-ring area of tumor shows more potential to grow and the central area tends to be dormant. The whole tumor tends to grow actively if inhibitors are neglected. Conclusion The existence of inhibitor is essential for the formation of necrosis. The stress of tumor cell phase drives the tumor to grow outside so that the high stress could be relieved.