  Two significant progresses have been made in the past years on our
understanding of hot accretion flows. One is that only a small fraction of
accretion flow available at the outer boundary can finally falls onto the black
hole while most of them is lost in outflow. Another one is that electrons may
directly receive a large fraction of the viscously dissipated energy in the
accretion flow, i.e, $\delta\sim 0.1-0.5$. The radiative efficiency of hot
accretion flow when these two progresses are taken into account has not been
systematically studied and is the subject of the present paper. We consider two
regimes of hot accretion model. One is the advection dominated accretion flows
(ADAFs) which lie on low accretion rate regime, $\la 10\alpha^2\ledd/c^2$;
another being the luminous hot accretion flows (LHAFs) which lie above this
accretion rate. For the latter, we assume that the accretion flow will has a
two-phase structure above a certain accretion rate, and a simplification is
adopted in our calculation of the dynamics. Our results indicate that the
radiative efficiency of hot accretion flow increases with the accretion rate
and is highly enhanced by the direct viscous heating to electrons compared to
the previous case of $\delta\ll 1$. When the accretion rate is high, the
radiative efficiency of hot accretion flow is comparable to that of the
standard thin disk. Fitting formulae of radiative efficiency as a function of
accretion rate for various $\delta$ values are presented.
