In this talk we show that if the normalized cocycle related to a quasiperiodic Jacobi operator H_{v,c} (where v being the potential and c being the off-diagonal term) is reducible to a constant rotation for almost all energies with respect to the density of states measure, then its dual model has either purely point spectrum for almost all phase or purely absolutely continuous spectrum for almost all phase, depending on the winding number of c. As a corollary, we obtain the complete phase-transition of extended Harper's model in the positive Lyapunov exponent region.