CRL 618 is a well-studied pre-planetary nebula. We have mapped its central region in continuum and molecular lines with the Sub-millimeter Array at 350 GHz at ~0.3-0.5 resolutions. Two components are seen in the 350 GHz continuum: (1) a compact emission at the center tracing the dense inner part of the HII region previously detected in a 23 GHz continuum and it may trace a fast ionized wind at the base; and (2) an extended thermal dust emission surrounding the HII region, tracing the dense core previously detected in HC3N at the center of the circumstellar envelope. It could result from a recent enhanced heavy mass-loss episode that ends the asymptotic giant branch phase. The isotopic ratios of sup 12C/sup 13C and sup 14N/sup 15N are 9 + or - 4 and 150 + or - 50, respectively, both lower than the solar values.