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This study is focused on the thermo-elastic structural topology optimization with multiple materials.The thermal stress coefficient (TSC) defined by the product between Young's modulus and thermal expansion coefficient is used to model the thermal stress load of multiple materials.The combination of UMMI (Uniform Multiphase Materials Interpolation) scheme and RAMP (Recursive Multiphase Materials Interpolation) model are used to parameterize the properties of multiple materials,including Young's modulus and TSC.Instead of adopting the common idea of using volume constraint,a new problem formulation with mass constraint is proposed.The linear mass constraint formulation which works well in static optimization problem is found sometime introducing a meaningless case in some elements.Therefore,a nonlinear mass constraint formulation is proposed by using the UMMI scheme to parameterize the density and an improvement scheme is suggested to obtain 0-1 solutions.Its validity is illustrated by numerical examples.Besides,the nonlinear mass constraint is theoretically proved having the advantage of increasing further the structural stiffness over the volume constraints with the predetermination of the same structure mass.