An adaptive iterative physical optics algorithm is proposed by studying the complex electromagnetic scattering characteristics of two dimensional multi roughness layered rough surface and target above, and a composite model of twodimensional layered rough surface and the target above is established by adopting the Monte Carlo method in combination with the generated Gaussian rough surface with Gaussian spectrum function based on sub regional modeling method. The direct induced electromagnetic current of the layered rough surface and the target is obtained by using the physical optics method and the equivalence principle. Based on the surface integral equations, the iterative mechanism of the coupled electromagnetic current between the layered rough surfaces and between the rough surface and the target is deduced. The traditional iterative physical optics method is improved by introducing the change rate of induced electromagnetic current energy, making the algorithm convergent automatically. The results are compared with those of the multilevel fast multipole algorithm and iterative physical optics method, and the accuracy and efficiency of the algorithm are verified. On this basis, the bistatic RCS calculation results and scattering characteristics of layered rough surfaces with different targets and different roughness are studied. The effect of the distance between layered rough surfaces and on the bistatic RCS calculation results and scattering characteristics is discussed. This study provides data support and theoretical basis for the detection, classification and recognition of ultra low altitude targets above a layered environment.