Granule electrostatics is widely found in most granule engineering areas. However, the working mechanism has never been fully understood due to its sensitivity to working conditions, such as granule geometrical shape (including length-ratio and front-facing angle), contact area, granule material, relative humidity, sliding velocity, sliding orientation, normal stress and so on. In this work, single granules were chosen to slide along a metal plate and the electrostatics charge generated were measured. The working factors above have been considered for two materials, i.e. PVC and coal. Regarding granule shape, it is found that granules with larger length-ratio tend to produce more electrostatics as well as the slender or sharper granules. Triangular granules generate more electrostatics than trapezoidal granules. In addition, electrostatics charge generation increases with decreasing granule front-facing angle and charges tend to gather at the granule tip. Regarding granule material, it is found that coal granule tends to generate more electrostatics in comparison with PVC granule. The sequence of the relative work function for the three materials used in this work from high to low is given as PVC, stainless steel and coal. Regarding surrounding factors, it is found that electrostatics increases with granule contact area and such trend increases with decreasing relative humidity. Electrostatics generated increases with decreasing relative humidity and sliding velocity. Granule sliding orientation does affect electrostatics. In this work, granules sliding with smaller front-facing angle as well as shorter side tend to generate more electrostatics. Electrostatics increases with normal stress. (c) 2020 Published by Elsevier B.V.