Abstract: Smart material structure is one of the hotspots in civil engineering field． The carbon black cement mortar was used as sensing element of concrete and nano-composite resin was used as sensing element of steel． With the study of two sets of smart beam experiments， the piezoresistive effect was researched． The results proved that the piezoresistive effect of sensing element was obvious in the beam under pure bending regions． It also proved that there existed the piezoresistive effect in shear moment regions of beams．