  A fundamental prediction of inflation is a nearly scale-invariant spectrum of
gravitational wave. The features of such a signal provide extremely important
information about the physics of the early universe. In this paper, we focus on
several topics about warm inflation. First, we discuss the stability property
about warm inflation based on nonequilibrium statistical mechanics, which gives
more fundamental physical illustrations to thermal property of such model.
Then, we calculate the power spectrum of gravitational waves generated during
warm inflation, in which there are three components contributing to such
spectrum: thermal term, quantum term and cross term combining the both. We also
discuss some interesting properties about these terms and illustrate them in
different panels. As a model different from cold inflation, warm inflation
model has its individual properties in observational practice, so we finally
give a discussion about the observational effect to distinguish it from cold
inflation.
