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The formation of hypercompact (HC) HII regions is an important stage inmassive star formation. Spectral line and continuum observations can exploreits dynamic conditions. We present high angular resolution observations carriedout with the Submillimeter Array (SMA) and the Very Large Array (VLA) towardthe HC HII region G35.58-0.03. With the 1.3 mm SMA and 1.3 cm VLA, we detecteda 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$_{3}$). G35.58-0.03consists of an HC HII core with electron temperature $T_e^*\geqq5500$ K,emission measure EM $\approx 1.9\times10^{9}$ pc cm$^{-6}$, local volumeelectron density $n_e=3.3\times10^{5}$ cm$^{-3}$, and a same width of radiorecombination line FWHM $\approx$ 43.2 km s$^{-1}$ for both H30$\alpha$ andH38$\beta$ at its intrinsic core size $\sim$3714 AU. The H30$\alpha$ line showsevidence of an ionized outflow driving a molecular outflow. Based on thederived Lyman continuum flux, there should be an early-type star equivalent toO6.5 located inside the HII region. From the continuum spectral energydistribution from 3.6 cm, 2.0 cm, 1.3 cm, 1.3 mm and 0.85 mm to 0.45 mm, wedistinguished the free-free emission (25% $\sim$ 55%) from the warm dustcomponent (75% $\sim$ 45%) at 1.3 mm. The molecular envelope shows evidence ofinfall and outflow with an infall rate 0.05 M$_{ \odot}$ yr$^{-1}$ and a massloss 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 andoutflowing gas per year. It is suggested that the infall is predominant and theenvelope mass of dense core is increasing rapidly, but the accretion in theinner part might already be halted.

Submillimeter Array and Very Large Array Observations in the Hypercompact HII region G35.58-0.03