Alkali basalts in Hannuoba area of northern Hebei are the major host rocks of deep-seated xenoliths and magacrysts. In addition, there are some alkali basalts containing no xenoliths and megacrysts and some tholeiites contain-ing xenoliths and megacrysts. This paper deals with the dynamic mechanism for the distribution of xenoliths and megacrysts on the basis of theoretical calculation. Xenoliths or megacrysts with densities larger than those of magmatic melts are mainly present in basaltic melts with large minimum settling radii(r*) and low settling velocities (U1 of xenoliths or megacrysts and high ascending velocities (U3). Spinel peridotite xenoliths are more abundant than transitional type peridotite xenoliths, green pyroxenite xenoliths are richer than black pyroxenite xenoliths, and clinopyroxene megacrysts are higher in content than garnet megacrysts, all related to large. r* and low U1 values of the formers.Anorthoclase megacrysts are obviously lower than host rocks in density and have very small minimum ascending radii. The larger the grain size, thehigher the ascending. velocity of anorthoclase. There fore, the anorthoclase occurring in basalts generally has comparatively large grain size.