We investigate precursors and predictability of extreme events of Lorenz system with different percentile. The precursors and predictability of Palmer Drought Severity Index (PDSI) extremes in China are analyzed, and obtained how the quality of the prediction depends on the size of the extreme events and on the correlation strength. Results indicate that for extreme events of Lorenz system and PDSI series, the stronger the extreme, the higher the predictablility. Moreover, we analyzed precursors and predictability of eight regions in China and provide some due scientific basis for flood and drought predictions.