Abstract: Considering the limitation of particle filter-target observation approach, the present study proposes a new target observation approach that can overcome this limitation. This new approach is then applied to the study of the predictability of El Niño-Southern Oscillation and reveals the sensitive areas for targeting observation associated with eastern-and central-Pacific El Niño events. By assimilating the target observations, the prediction uncertainties for the two types of El Niño events are significantly reduced. This result confirms that the sensitive areas revealed by the new approach, compared with other areas, can play a much more important role in improving the El Niño forecast skill.