Flory's lattice theory has been applied to the polymer blends containing a thermotropic liquid crystalline polymer (LCP) and flexible chain polymers. The phase behavior of blends of a thermotropic LCP and a flexible chain polymer at melt processing temperature can be evaluated by two quantitative parameters: the polymer-polymer interaction parameter (chi (12)) and the degree of disorder (y/x(1)). From the results of the model calculation, it has been found that the miscibility is increased with the increase of the degree of disorder (y/x(1)) of the LCP and with the decrease of the degree of polymerization (x(1)m and/or x(2)) The simulated spinodal curve of ternary polymer blends containing a thermotropic LCP and two flexible chain polymers has been calculated using the lattice theory. When three pairs of binary polymer blends are immiscible, the coexistence curve of the three phases appears for the ternary blend having similar values of Xi, among component polymers. When the LCP is immiscible with two flexible chain polymers, and also when the two flexible chain polymers are miscible with each other, the strong effect of anisotropy of the LCP is observed in the simulated spinodal curve. When three pairs of binary polymer blends are miscible, a phase separation is also observed due to the \Delta chi\ effect.