  Motivated by recent progress in our understanding of the $B$-mode
polarization of cosmic microwave background (CMB), which provides important
information about the inflationary gravitational waves (IGWs), we study the
possibility to acquire information about the early universe using future
space-based gravitational wave (GW) detectors. We perform a detailed
statistical analysis to estimate how well we can determine the reheating
temperature after inflation as well as the amplitude, the tensor spectral
index, and the running of the inflationary gravitational waves. We discuss how
the accuracies depend on noise parameters of the detector and the minimum
frequency available in the analysis. Implication of such a study on the test of
inflation models is also discussed.
