The problem of controlling extreme events in spatially extended dynamical systems based on the observation only is studied in this paper. The control method we proposed locally changes parameters of the system in the vicinity of the localized high-amplitude events continuously，without needs of system model and prediction. Considering the specific Complex Ginzburg-Laudau equation based model，we provide theoretical analysis for choosing the effective parameters to achieve the control. Numerical simulations and statistic analysis demon-strate that extreme events can be efficiently suppressed by our strategy with a low cost. In particular，the tolerant limit of observation error and time delay in applying the control are also addressed.