The invention relates to a method for online activity recovery of heavy oil hydrotreatment catalysts, and a catalyst unloading method. The ethod comprises the following steps: gradually replacing a heavy oil raw material for feeding with a carrying oil, carrying out reaction after the replacement is completed, and then switching the heavy oil raw material for introduction into a reactor, wherein the carrying oil contains an additive, and the additive is an organic matter with hydrogen supply effect and/or a carbon deposit dissolving effect. After online activity recovery is carried out by adopting the method, the surface carbon deposition of catalysts can be reduced, the catalyst activity is effectively recovered, the catalyst utilization rate is improved, the operation period is remarkably prolonged, and economic benefits are obvious; before waste catalyst unloading, the catalyst unloading method is added in a conventional catalyst unloading operation, so that the waste catalyst can be unloaded more conveniently, and the device shutdown time is shortened.