To analyze the dependence of the DC stress negative bias temperature instability (NBTI) effect on basic device paraments, such as the channel length, the gate oxide thickness, the doping concentration, we solve the hydrogen molecule drift-diffusion model of NBTI together with the semiconductor device equations. The results are compared with the existing experimental data and the basic laws and physics of devices, which is necessary for reliability studies of NBTI. The analysis results show that NBTI effect is not affected by the channel length change, but maily by the thickness of the gate oxide layer. Gate oxide thickness thinning and gate oxide layer electric field enhancement effect are consistent, which determines the device degradation in the manner of exponential law. With channel doping concentration increasing, NBTI effect will be reduced, which is because the device channel surface hole concentration is reduced, however with the doping concentration increases to such a value that the device source drain leakage current is very low (low leakage device), the MBTI effect is obviously enhanced. These are helpful for understanding NBTI and designing the high performance device.