To investigate the relationship between the falling angle constrained guidance law with the precision of the air-to-ground guided weapons, the three-dimensional guidance law with falling angle constrain was demonstrated. Geometric analysis methodology and the optimal solution to linear quadratic problem were presented to obtain the influence of the falling angle on the terminal guidance command and the miss distance. The Monte Carlo simulation was conducted, it was shown that falling angle constrain guidance law can mitigate the effect of height measurement error and improve the impact precision.