In this paper, a modified polynomial guidance law is studied for a powered terminal descent of a lunar lander. Also, Zero-Effort-Miss/Zero-Effort-Velocity (ZEM/ZEV) and modified Apollo guidance laws including off-line trajectory optimization approach are analyzed. Because each guidance law has advantages and drawbacks, modified polynomial guidance law is proposed. The modified guidance law is derived quasi-analytically after taking advantages of previous real-time guidance laws for onboard application. In the numerical simulation section, performance will be compared from several points of view such as avoiding surface collision and fuel consumption.