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Brillouin lasing has been widely applied to microwave oscillators, optical gyroscopes, optical sensors, and other fields owing to its strong and flexible dynamics. Microspheres with ultrahigh quality factors and small mode volume are very suitable for generating Brillouin lasing, but it is difficult to integrate them on a chip. Here, we utilize subwavelength grating waveguide as a photonic coupler to connect the silica microsphere with a silicon chip and realize on-chip backward Brillouin lasing. It is experimentally indicated that when the on-chip pump power reaches 24.8 mW, the backward Brillouin lasing with an on-chip slope efficiency of 5% will be excited. Our method makes it easier to realize on-chip Brillouin acousto-optic interaction and greatly expands the application range of microspheres.