Abstract: A localized small force provides a unique non invasive probe based on both the structure of the force chain network and the response of granular matter. In this work, quasistatic packings of 30\,000 spherical particles confined within a 2m*1m*0.01m container are simulated by using discrete element method. The sizes of particles are 0.01m, 0.008m and 0.006m, respectively, and the number of particles of each size is 10 000. A localized force is exerted on one of the top layer particles with a small magnitude of 5.2*10^ - 2N, which is 100 times of the weight of the largest particle with the size of 0.01\,m in order to ensure that the granular material keeps still. The results show strong heterogeneous pathways of force propagation and the fluctuations of force are evident. With the increase of the distance from the exerted particle, the force fluctuations are reduced. The calculated stress values agree with the Flamant solutions of stress as the distance is more than 5 times the size of the largest particle. The effect of surface friction of particles is discussed. The preliminary results indicate that a larger friction coefficient leads to more uniform stress distributions.