The feasibility and availability of applying ensemble Kalman filter (EnKF) technique in convective scale systems were demonstrated by an observation system simulation experiment (OSSE) in this paper, which assimilates simulated radial velocity and reflectivity of one Doppler radar with an EnKF assimilation system based on WRF model. The experiment shows: the assimilation system has the ability to accurately analyze the detailed characters of flow fields, thermodynamic and microphysical fields of the storm, forecast and analysis errors of almost all variables decrease significantly after assimilation cycles, and forecast fields of all levels can be improved by assimilation, especially on levels of larger errors. Reliable correlativity between radar reflectivity, radial velocity observations and forecast fields can be established after 8 assimilation cycles, and the background error covariance has a complex structure and is highly inhomogeneous, anisotropic and flowdependent. Determinate forecast of ensemble mean field can keep the detail characters of truth storm in short period but errors grow fast.