A method for evaluating the effectiveness of electro-optical jamming device on laser rangefinder was proposed in this paper. The evaluation rules of jamming effectiveness for laser range deception jamming and laser blinding jamming on laser rangefinders were presented in detail. For laser range deception jamming, whether the ranging error of a laser rangefinder under jamming is greater than three times its ranging accuracy (standard de?viation) without jamming is proposed as the criterion for whether the jamming is effective or not. The jamming effects can be graded into several jamming rates according to the jamming success rates. For laser blinding jam?ming on a laser rangefinder, the jamming effects can be graded into four jamming rates according to the degrees of damage to the ranging accuracy or ranging capability of the laser rangefinder.