Workspace Measurement Position System (wMPS) is a newly developed system based on multi-directional positioning principle. Initially, the angular measurement model was proposed for angle uncertainty of the transmitter. The uncertainties in the vertical and horizontal angles were analyzed and a feasible method for estimating the uncertainty of parameters was proposed. Then, the uncertainty of parameters was propagated from the angular measurement model using Monte Carlo simulation and the angular uncertainty distribution was determined by the simulation. Finally, horizontal angle uncertainty evaluation platform based on polygonal prism and collimator was designed by using angle dividing table as angle reference. Experiments were then carried out to determine the actual uncertainty in the horizontal angle. Results show that the platform is effective and horizontal angle uncertainty is about 2.2″ in the working space.