The power spectrum of the scalar-tensor inflation with a quadratic form Ricci scalar coupling function \(\Omega(\phi)=1- 2\phi/\phi_c+(1+\delta^2)(\phi/\phi_c)^2\) can be enhanced enough to produce primordial black holes and generate scalar-induced gravitational waves. The masses of primordial black holes and the frequencies of scalar-induced gravitational waves are controlled by the parameter \(\phi_c\), and their amplitudes are determined by the parameter \(\delta\). Primordial black holes with stellar masses, planetary masses, and masses around \(10^{-12} M_\odot\) are produced and their abundances are obtained from the peak theory. The frequencies of the corresponding scalar-induced gravitational waves are around \(10^{-9}\) Hz, \(10^{-6}\) Hz, and \(10^{-3}\) Hz, respectively. The primordial black holes with masses around \(10^{-12} M_\odot\) can account for almost all of the dark matter, and the scalar-induced gravitational waves with frequencies around \(10^{-9}\) Hz can explain the NANOGrav 12.5yrs signal.