  In the physics of solar flares, it is crucial to diagnose the physical
conditions near the flare energy-release sites. However, so far it is unclear
how do diagnose these physical conditions. Solar microwave type III burst is
believed to be a sensitive signature of the primary energy release and electron
accelerations in solar flares. This work takes into account the effect of
magnetic field on the plasma density and developed s set of formulas which can
be used to estimate the plasma density, temperature, magnetic field near the
magnetic reconnection site and particle acceleration region, and the velocity
and energy of electron beams. We applied these formulas to three groups of
microwave type III pairs in a X-class flare, and obtained some reasonable and
interesting results. This method can be applied to other microwave type III
bursts to diagnose the physical conditions of source regions, and provide some
basic information to understand the intrinsic nature and fundamental processes
occurring near the flare energy-release sites.
