A rheo-optical experimental apparatus based on Phase Modulated Flow Birefringence(PMFB) method has been developed. This PMFB method is one of the roost powerful techniques to study the theological behaviors of a polymer system. An useful computer-aided system which has the capability of controlling the flow dynamics, signal detections and data acquisitions for the PMFB method has been developed. Also a newly modified mathematical calculation method to obtain the birefringence with less error propagations has been established. This computerized system for PMFB technique was carefully checked by the quarter wave plate calibration procedure and was proved to he reasonable for obtaining the rheo-optical properties of the polymer liquids. Also, with the PMFB method, an experiment for investigating the effects of molecular weight on the theological properties of l.5 wt% a of polystyrene solutions was carried out. The experimental results were in good agreement with the general viscoelastic properties of the polymer solution and with the other experimental results reported so far.