With high duty cycle and wide aperture, the Large High Altitude Air Shower Observatory - Water Cherenkov Detector Array(LHAASO-WCDA) can conduct an unbiased gamma-ray sky survey in the energy range from a few hundred GeV to 100 TeV. The sensitivity of WCDA is as high as a few percent of Crab units, which allow us to monitor the VHE variability of blazars. The LHAASO Collaboration has developed an online monitoring program to monitor the extragalactic VHE flare in the WCDA’s field of view. Once a flare exceeding the threshold is detected, an alert will be sent to other instruments automatically, and a follow-up multiwavelength observation could be carried out. In this paper, the current status of the monitor, the candidate sources, background estimation method, data reduction, testing running result are presented.