This paper provides the target observability analysis of advanced guidance laws such as the impact angle control guidance law and the time-to-go polynomial guidance law. The target observability condition for a constant-velocity target, which is given by the function of line-of-sight(LOS) angle, is considered. To analyze the target observability under advanced guidance laws, the closed-form solution of LOS angle produced by these laws is firstly derived and substituted into the predetermined observability condition. The analysis result shows that the target observability of advanced guidance laws is depending on the choice of guidance gain and the initial engagement geometry. Finally, this mathematical analysis result is evaluated and demonstrated by number of simulation.