  We perform a next-to-leading-order QCD analysis to world data on polarized
structure functions $g_1$ and $g_2$ in a fixed-flavor number scheme. We include
target mass corrections and higher twist effects in our fitting procedure and
study their non-negligible effects on physically interesting quantities.
Twist-3 contributions to both polarized structure functions are determined, and
the accuracy of the extracted polarized parton distribution functions is
improved. $^{3}\rm He$ and $^{3}\rm H$ polarized structure functions are
described based on our fit result. Moreover, sum rules are derived and compared
with available theoretical and experimental results.
