A novel method based on the nonlinear equation of airborne lidar is proposed for determining the boundary value of the extinction coefficient for atmosphere aerosol in lower atmosphere.In the method the mathematical relation between the boundary value of the extinction coefficient and the lidar return signals is firstly deduced from the lidar equation.The relation is expressed by a nonlinear equation with the boundary value of the extinction coefficient as a variable to be determined.Then,the equation is solved numerically using the improved Jarratt iteration.The boundary value of the extinction coefficient for atmospheric aerosol is hence obtained.The method is used for the return signals of the airborne lidar.Which are obtained using the real return signals of the ground-based lidar.The obtained results are compared with those obtained using the ramp method.The results show that the relative error of boundary value of the extinction coefficient obtained using our method is smaller by 5.9% than that using the ramp method.In our method only three times of iterations are required due to the six-order convergence property.No auxiliary equipment is needed.The method may explore a large number of applications because of its high precision and fast convergence.