  We investigate the second order gravitational waves induced by the primordial
scalar and tensor perturbations during radiation-dominated era. The explicit
expressions of the power spectra of the second order GWs are presented. We
calculate the energy density spectra of the second order GWs for a
monochromatic primordial power spectra. For large $k$ $\left( k>k_* \right)$,
the effects of the primordial tensor perturbation with tensor-to-scalar ratio
$r=A_{h}/A_{\zeta}=0.2$ lead to an around $50\% $ increase of the
signal-to-noise ratio (SNR) for LISA observations.
