Based on the finite difference time domain/multi-resolution time domain (FDTD/MRTD) method, composite scattering between slightly rough optical surface and buried multi-body defect particles was researched. The concept of multi-body defect particles is put forward and the composite scattering model of slightly rough optical surface and buried particles is established. The computational domain is divided into MRTD method domain and FDTD method domain based on displacement interpolation principle of DB2 wavelet scale function, and the composite scattering field is deduced. Composite scattering cross sections of buried multi-body particles are discussed in detail. Results are compared with those obtained with the method of moment, and they are found to be consistent very well, thereby proving the reliability of the proposed method. The effects of incidence angle, sphere number and sphere separation distance on composite scattering are studied. The study will provide technological support for the fields of nondestructive examination, optical film, optical performance design of micro- and nano- structures etc.