The triaxial， scanning electron microscrope and X-ray diffraction tests had been made to investigate the bentonite content on macroscopic and microscopic properties of plastic concrete with a view to revealing the mechanism of macro-mechanical behavior from micro-scale. The results show that increasing the bentonite content makes the material behavior act like the ductile materials with expansion deformation decrease. The bentonite content increase results in decrease of the peak stress and increase of the peak strain and the modulus-strength ratio. The cohesion increases at first and then weakens， while the trend of internal friction angle is opposite to cohesion. According to the result of micro-tests， the more pore channels exist with the higher addition of bentonite which reflect the attenuative effect on macro-strength. Furthermore， low bentonite content will be liable to fill voids in aggregate and weakens the particle angularity. The superabundance of bentonite dosage causes the poor bond and increase of roughness of particles. The influence of bentonite on the macro-mechanical properties of plastic concrete is mainly attributed to the synergistic effect of plasticization by increasing the particle pore， and solidification by filling the particle gaps.