  We constrain the cosmological parameters from cosmic microwave background
(CMB) and gravitational wave observations. We not only combine LIGO
observations with CMB to measure cosmological parameters, but also forecast the
potential abilities of the LISA detector and PTA projects. In the
$\Lambda$CDM+$r$ model, the constraint from BK15 and FAST projects have a
significant impact on tensor-to-scalar ratio.
