Aimed at the problems that the shielding effects of conecylinder ballistic target exists in the process of observation, the concrete location of the boundary between the shielding area and the visible area can be made a thorough inquiry, and a novel algorithm is proposed to judge whether the scatter is shielded or not. First, a mathematic model of echo based on the observation in narrowband radar is built. Then, a model of sliding scatters of the cone cylinder ballistic target is built, and the characteristic of each scatter is analyzed. Finally, this paper looks into the causes of the shielding effects, analyzes the location of the boundary between the shielding area and the visible area, and proposes a novel algorithm to judge if the scatter is shielded. The simulation shows that the microDoppler curves of ideal scatters and sliding scaffers are different and shielding effects will result in the francation phenomenon of the microDoppler curves with the change of observation angles, which proves that the conclusion of this article is right and the algorithm is effective. And this provides a reference for the feature analysis of ballistic target being shielded.