The impact of the assimilation of bogus vortex on the typhoon numerical simulation using the MM5 four-dimensional variational data assimilation system is studied in this paper.A series of 48 h simulations are conducted for typhoon Phanfone.The results show that: assimilation of the bogus vortex variables is more effective than the traditional method which implants a synthetic vortex into the background conditions.Simultaneous assimilation of the bogus wind, pressure, temperature and specific humidity data has less positive impact than that of the bogus pressure and any one of other variables.An initial vortex which has a clearer structure and is more consistent with the environment flow is obtained by assimilating the bogus specific humidity and pressure data.