The reinforcement of soil shear strength by nylon net as substitute materials simulating a fine root system was evaluated by soil strength parameters(apparent cohesion(c) and internal friction angle(tan${phi}$), using simple shear tester which clearly depicts shear deformation and controls soil suction. And the results of shear test by using bamboo as a substitute materials simulating a main root system and using nylon net as a substitute materials simulating a fine root system were compared. The reinforcement of soil strength by nylon net are expressed by apparent cohesion more than internal friction angle. In addition the increment of apparent cohesion by nylon net reached a peak in suction 60 $cmH_2O$. Different from with bamboo, the possibility of the change on internal friction angle(tan${phi}$) caused by the soil water condition was shown in shear strain 20% condition. These results show that the mechanism of reinforcement by substitute materials simulating root system may be different in the condition of various soil water content.