A novel and simple method used for the measurement of the practical value of the retardance (an overall ambiguity modulo 2π is not considered) and the determination of the fast or slow axis of a quarter-wave plate employing two polaroids and a right-angle prism is reported. The theoretical analysis of the principle is given taking Jones matrix as a mathematical tool, the uncertainty of formula is derived, the effects of each factor upon the uncertainty are simulated using a computer. The working conditions of this method are discussed. An application example is given, and the measured result of the example is verified with results of test and computer simulation, which indicates that the method is feasible. Furthermore, this method has the advantages such as easier to obtain the optical devices needed, simpler to operate, and accurate etc.