Natural pumice from inner Mongolia region was used as coarse aggregate. And rubber crumb modified by span 40 in order to study the influence of modified rubber crumb on mechanical characteristics to lightweight aggregate concrete. With using the nuclear magnetic resonance(NMR) technique, the influence modified rubber crumb the macroscopic performance of lightweight aggregate concrete the porosity of lightweight aggregate concrete and transverse relaxation time T2. Then technique means such as mechanical property test, BT 1800dynamic image particle test, hydrophilic test, environmental scanning electron microscope test and so on to make comparison and argument between technique means and NMR results. The results show that mechanical property of lightweight aggregate concrete is enhanced and modifier improves rubber crumbs hydrophilic property and circularity. Besides, 3 peaks of nuclear magnetic resonance T2 spectrum move toward the small pore and porosity of lightweight aggregate concrete decreases by 11%.