Lottery promotion has been widely used as an effective and practical means of promotion.  However, most relevant research have focused on the impact of single promotion and consumers' lucky wins on subsequent purchase decisions.  This study is based on the marketing placebo theory and the reaction expectation theory, focusing on the impact of the number of unwinning prizes on the purchase intention of innovative products under the lottery promotion.  Experiment 1 verifies the effect of the number of unwinning prizes in the sweepstakes promotion on the placebo effect of the doom.  Experiment 2 explores the  impact of the number of unwinning prizes on the purchase intention of innovative products under the lottery promotion.  Experiment 2 also reveals the chain mediation mechanism of negative emotion and perceived risk.  Experiment 3 reveals that the controllability of promotional lottery perception plays a regulatory role in the impact of the number of unsuccessful draws on the willingness to  purchase innovative products.  This study expands the theory of placebo effect and provides practical guidances for  enterprises to apply sweepstakes and promotions to improve corporate performances.