In order to study the in-plane displacement of curved bridge under thermo load, a class of equations for in-plane displacements of curved beams with various end restrictions under thermo load are derived explicitly, based on the principle of thermal expansion and theory of virtual work. In the case of infinite limit of radius, these equations coincide with that of the straight beams. Compared with the results of FEM, the analytical solutions by the proposed formulae are accurate. A real multi-span curved bridge subjected to concentrated loads caused by the friction force on the top of bridge piers and thermo load due to temperature difference is analyzed by using the newly derived equations as well as FEM. The agreements further suggest the practicability of the proposed theory. The analytical solutions obtained in this paper would provide a scientific base for further study and design of the curved bridges.