  We have accurately measured the bispectrum for four scale-free models of
structure formation with the spectral index $n=1$, 0, -1, and -2. The
measurement is based on a new method that can effectively eliminate the alias
and numerical artifacts, and reliably extend the analysis into the strongly
non-linear regime. The work makes use of a set of state-of-the art N-body
simulations that have significantly increased the resolution range compared
with the previous studies on the subject. With these measured results, we
demonstrated that the measured bispectrum depends on the shape and size of
$k$-triangle even in the strongly nonlinear regime. It increases with
wavenumber and decreases with the spectral index. These results are in contrast
with the hypothesis that the reduced bispectrum is a constant in the strongly
non-linear regime. We also show that the fitting formula of Scoccimarro &
Frieman (1999) does not describe our simulation results well (with a typical
error about 40 percent). In the end, we present a new fitting formula for the
reduced bispectrum that is valid for $-2 \leq n \leq 0$ with a typical error of
10 percent only.
