In this paper, the dark current-voltage characteristics of p-n junction of silicon solar cells are analysed, with different nickel film thicknesses of 200nm, 400nm and 600nm. The formation of nickel silicide is obtained after the thermal annealing process for 1min, 5min and 10min. The dark current-voltage curves obtained by three kinds of annealing temperature as a function of time are achieved in experiment. The improvement of series resistance extracted from the dark current-voltage curve in the upper voltage range is observed. The influence of nickel film thicknesses on dark current-voltage characteristics of silicon solar cells is confirmed.