The Water Cherenkov Detector Array (WCDA) is an important component of Large High Altitude Air Shower Observatory (LHAASO). The main scientific target of WCDA is continuously surveying the northern sky at the level of few percent of Crab unit. In this proceeding, based on its first year data of WCDA-1 data, the result about the Crab Nebular observation and its energy spectrum measurment have been presented. And with WCDA full array data taking since Mar. 2021, some preliminary results have been reported.