Beam splitter is one of the most important components in long trace profiler. A new beam splitter which is composed of two Fresnel biprisms is proposed. An incident beam is divided into two parallel exiting beams with a variable separation, equal-intensity and zero optical path difference. The characteristics of the Fresnel biprisms is described in detail. The amplitude pattern and intensity pattern of interference fringes made by two exiting beams in detector is analyzed and simulated. The result of analysis and simulation suggests that the Fresnel biprisms not only owns the same function of four existing equal amplitude-splitting beam splitters but also can obtain high accuracy. We comparing the performance of the Fresnel biprisms with four existing equal amplitude-splitting beam splitters, and the result states that the Fresnel biprisms simultaneously own many merits including simple structure, zero optical path difference and variable separation with the exiting beams and so on. It can be a substitute for the existing amplitude-splitting beam splitters.