New wide single mode strip and grating loaded waveguide on thin silicon-on-insulator CMOS compatible structure is proposed and analyzed. Waveguide is built by silicon nitride strip and gratings placed on silica cover of slab silicon. This structure is similar to conventional strip-loaded waveguide but differs by additional gratings near the strip sides. Numerical 3D simulations by FDTD and BPM prove that the side gratings with period 0.6 microm and depth 0.16 microm provide the high Figure of merit for higher order mode suppression and built quasi-single-mode waveguide with mode size approximately 10 microm and propagation loss approximately 0.3 dB/cm.