The production of GWs during preheating in the Starobinsky model with a nonminimally coupled auxiliary scalar field is studied through the lattice simulation in this paper .
We find that the GW spectrum \Omega _ { gw } grows fast with the increase of the absolute value of coupling parameter \xi .
This is because the resonant bands become broad with the increase of | \xi| .
When \xi < 0 , \Omega _ { gw } begins to grow once the inflation ends and grows faster than the case of \xi > 0 . \Omega _ { gw } reaches the maximum at \xi = -20 ( \xi = 42 for the case \xi > 0 ) and then decreases with slight oscillation .
Furthermore we find that the GWs produced in the era of preheating satisfy the limits from the Planck and next-generation CMB experiments .