Smokescreen is effective to counter infrared reconnoiter and guide. In order to assess and evaluate the ability of smokescreen to interfere IR imaging quantificationally, study was carried out both in theory and in experiment. Firstly, based on discrimination distance rule, the equation to calculate the view range of IR imaging under the interference of smokescreen was built from the aspect of radiation contrast, which made the analysis and evaluation of interference effect of smokescreen available from assessing the variation of view range of IR imaging before and after the interference. Secondly, transmissivity of smokescreen to different wavebands was measured in experiment. And then human body was selected as the target to observe. Normalized mutual information was selected as criterion based on correlativity rule and direct observation was used to analyze the interference effect of smokescreen on IR imaging in experiment. The results show that under the action of smokescreen, the apparent contrast between the target and background has dropped to less than 4% of their inherent contrast when the IR imaging system can′t satisfy the demand of recognition. The corresponding transmissivity of smokescreen was 55%, and the theoretical calculation was consistent with the experimental analysis.