To satisfy the demands of bearing capacity and loading space for large-scale heavy-load motion simulation, a family of novel roll-pitch platform mechanisms with a virtual rotation axis are synthesized based on the principle of equivalent substitution of kinematic chain and the existence condition of rotation axes in parallel mechanisms. The structure features and DoF (degree of freedom) properties of the roll-pitch platform mechanism are analyzed by using constraint-screw system discriminance. On the basis of actuating selection, kinematic and dynamic models of the 2-RP
U mechanism, a representable type of this family, are derived by screw theory. A numerical example is applied to analyzing a type of mechanism with prospects for engineering applications. This mechanism not only has large loading space, but also can realize static-load balancing, which will be available for large-scale heavy-load motion simulation platform.