The characteristic parameters quality factor and reverse saturated current of photovoltaic detectors have very big distinction since different manufacture handicraft and producing conditions. A indirect method of measuring semiconductor PN junction characteristic parameters is proposed, and the convergence property of the numerical computational method used in this method is proved. Two simplified analysis formulas on using open circuit voltage and short circuit current are proposed to calculate PN junction quality factor and reverse saturation current of the photocell. Compared with the results of the numerical computational method, the relative error of quality factor and the reverse saturated current calculated by the simplified analytical formula are 0.03% and 0.25%, respectively. Compared with experimental results, the relative errors of open-circuit voltage calculated with iterative method is not less than 0.3%.