Though the single phase martensite of low alloy steel usually has a total elongation less than 5% and cannot directly apply to the commercial steel sheets, the multilayered austenite-martensite steel composites can achieve more than 1.2GPa tensile strength and 20% uniform elongation. It is believed the multilayered austenite plays an important role on the ductility improvement of martensite. To clarify the martensite ductility improvement mechanism and describe the heterogeneous deformation behavior of multilayered austenite-martensite steel composites including the interphase and intergranular strain partitioning, in situ neutron diffraction study during uniaxial tensile deformation was carried out by using the ENGIN-X to evaluate the lattice strain and crystallographic orientation evolutions.