When the radar seeker is detecting ultra low altitude targets, it is affected by multipath effects, which will greatly reduce the tracking accuracy. When the line of sight (LOS) angle is constrained near the Brewster angle, it can effectively reduce the influence of multipath interference. Based on the integral sliding mode control principle, a linear integral sliding mode guidance law is designed. Compared with traditional sliding mode guidance laws, this guidance law has faster asymptotic convergent property because it saves the phase of approaching the sliding surface. To further improve the convergence rate of the LOS angle, a nonlinear integral sliding mode guidance law is designed. This guidance law can guarantee that the LOS angle converges to the Brewster angle fastly in finite time. To solve the chattering problem caused by the high gain coefficient of the integral sliding mode switch term, a sliding mode disturbance observer is designed to estimate the maneuvering acceleration of the target. Combining the nonlinear integral sliding mode guidance law and introducing the estimated value of target acceleration, a composite guidance law is designed. The simulation results show that the composite guidance can effectively eliminate the chattering phenomenon, reduce the miss distance and improve the accuracy of intercepting.