The invention discloses an integrated adsorbent activation and spraying demercuration method which comprises the following steps: monitoring the mercury concentration of flue gas in real time by virtue of an online mercury concentration monitor (6), and dynamically regulating a second regulating valve (10) to control the injected volume and injection rate of a mercury adsorbent; dynamically regulating a third regulating valve (14) to control the injected volume and injection rate of compressed air; meanwhile, dynamically regulating a first regulating valve (7) on an online activation mechanism to control the injected volume and injection rate of an active component precursor; activating the adsorbent on line; spraying and injecting the activated adsorbent into a flue through a spraying mechanism, thereby implementing demercuration of the flue gas. According to the method, the demercuration performance of the adsorbent is optimized, active component waste is also avoided, the using amount of the adsorbent is reduced, and the demercuration cost is greatly reduced; in addition, the mercury adsorbent is activated on line in real time, and the method is adapted to frequent fluctuation of the mercury concentration.