In this paper, based on the equivalent single diode circuit model of the solar cell, an equivalent circuit diagram for two serial solar cells is drawn. Its equations of current and voltage are derived from Kirchhoff's current and voltage law. First, parameters are obtained from the I-V (current-voltage) curves for typical monocrystalline silicon solar cells (125 mm x 125 mm). Then, by regarding photo-generated current, shunt resistance, serial resistance of the first solar cell, and resistance load as the variables. The properties of shunt currents (I-sh1 and I-sh2), diode currents (I-D1 and I-D2), and load current (I-L) for the whole two serial solar cells are numerically analyzed in these four cases for the first time, and the corresponding physical explanations are made. We find that these parameters have different influences on the internal currents of solar cells. Our results will provide a reference for developing higher efficiency solar cell module and contribute to the better understanding of the reason of efficiency loss of solar cell module.