  The formation of hypercompact (HC) HII regions is an important stage in
massive star formation. Spectral line and continuum observations can explore
its dynamic conditions. We present high angular resolution observations carried
out with the Submillimeter Array (SMA) and the Very Large Array (VLA) toward
the HC HII region G35.58-0.03. With the 1.3 mm SMA and 1.3 cm VLA, we detected
a total of about 25 transitions of 8 different species and their isotopologues
(CO, CH$_3$CN, SO$_2$, CH$_3$CCH, OCS, CS, H, and NH$_{3}$). G35.58-0.03
consists of an HC HII core with electron temperature $T_e^*\geqq5500$ K,
emission measure EM $\approx 1.9\times10^{9}$ pc cm$^{-6}$, local volume
electron density $n_e=3.3\times10^{5}$ cm$^{-3}$, and a same width of radio
recombination line FWHM $\approx$ 43.2 km s$^{-1}$ for both H30$\alpha$ and
H38$\beta$ at its intrinsic core size $\sim$3714 AU. The H30$\alpha$ line shows
evidence of an ionized outflow driving a molecular outflow. Based on the
derived Lyman continuum flux, there should be an early-type star equivalent to
O6.5 located inside the HII region. From the continuum spectral energy
distribution from 3.6 cm, 2.0 cm, 1.3 cm, 1.3 mm and 0.85 mm to 0.45 mm, we
distinguished the free-free emission (25% $\sim$ 55%) from the warm dust
component (75% $\sim$ 45%) at 1.3 mm. The molecular envelope shows evidence of
infall and outflow with an infall rate 0.05 M$_{ \odot}$ yr$^{-1}$ and a mass
loss rate $5.2\times10^{-3}$ ${\rm M_{ \odot} yr^{-1}}$. The derived momentum
($\sim0.05$ M$_{\odot}$ km s$^{-1}$) is consistent between the infalling and
outflowing gas per year. It is suggested that the infall is predominant and the
envelope mass of dense core is increasing rapidly, but the accretion in the
inner part might already be halted.
