Martensitic phase transformation (PT) is a first-order phase transformation, with change in the relative positions of atoms and without diffusion, which plays an important role in the formation of nano and microstructures and mechanical properties in many materials such as shape memory alloys. In this study, the coupled system of the phase field and elasticity equations for multivariant martensitic phase transformations including heterogeneity and anisotropy effects of austenite and martensitice variants is presented. The finite element method and the COMSOL code are used to solve the system of equations for plane stress problems. Several numerical examples of thermal, stress, and surface-induced phase transformations for single and two martensitic variants are presented including plane interface propagation, growth of a preexisting nucleus for single and two variants, formation of a martensitic-martensitic interface for two martensite variants, PT in the presence of holes and so on. The significant effect of heterogeneity and anisotropy on the PT was revealed especially in the presence of thermal strains so that the martenstic nucleation, initial growth, transformation path and the final nanostructure can be remarkably different. Keywords: Phase Transformation, Nano Dimension, Phase field, Comsol, Anisotropy and Hetergenous, Thermal Strain