The effect of pressure on the tricritical point (TCP) of a ternary system, polystyrene (PS) I+PS II+methylcyclohexane, was studied by numerical analysis of the generalized Flory-Huggins equation for the Gibbs free energy. For the ternary system, the molecular weight of PS II M(2t), total volume fraction of PS phi(st), volume fraction of PS II with respect to total volume of PS xi(2t), and temperature T-t at TCP were calculated for various values of the molecular weight of PS I M(1) in the pressure range from 0 to 100 MPa. As M(1) increases, the ratio r(t)= M(2t)/M(1) and phi(st) decrease, while T-t and xi(2t) increase monotonically irrespective of p. The curves of r(t) and phi(st) vs p have a maximum, while the curves of T-t and xi(2t), vs p have a minimum, irrespective of M(1). For small M(1) these curves are nearly flat and roughly symmetrical with respect to the extrema. From these calculated results it is predicted that the tricritical solution at atmospheric pressure remains very near the tricritical state along the cloud-point curve in the temperature vs pressure diagram.