  In this paper we describe an experiment of efficient cooling of $^{87}$Rb
atoms in two-frequency diffuse laser lights. Compared with single frequency
diffuse light, two-frequency diffuse lights have wider velocity capture range
and thus can cool more atoms. In our experiment, the maximum number of cooled
atoms can reach up to $3.9\times10^9$. Such a result is quite useful in
building a compact cold atom clock.
