The effects of design parameters for small scale hydro power(SSHP) plants due to rainfall condition have been studied. The model to predict hydrologic performance for SSHP plants is used in this study. The results from analysis for rainfall conditions based on KIER model show that the capacity and load factor of SSHP site had large difference between the period. Especially, the hydrologic performance of SSHP site such as design flowrate due to rainfall condition of recent period varied sensitively. And also, the methodology represented in this study can be used to decide the primary design specifications of SSHP sites.