The　optimization　of　lunar　soft　landing　trajectory　is　an　optimization　control　problem　with　non-linear　free　terminal　time　and　control　constrained　The　application　of　the　Chebyshev　pseudospectral　is　described　on　the　optimal　control　problems.　This　method　employs　Nth　Lagrange　polynomial　approximations　for　the　state　and　control　variables　to　transform　the　state　differential　equations　to　algebraic　equations.　Finally　the　optimal　control　problem　is　transformed　to　a　nonlinear　programming　problem.　In　process　of　solving　the　optimal　control　problem　using　matlab,　control　variables　and　flying　time　are　used　as　optimal　variables.　Simulation　results　demonstrare　the　methodology　for　the　optimal　trajectory　designing　has　strong　convergence.　©　2011　IEEE.