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With the continuing requirement of the structural displacement monitoring for massive civil structures, a vision-based displacement monitoring system is gaining great attention as an inexpensive solution. Currently, a visually servoed paired structured light system (ViSP) which measures the relative translational and rotational displacement each in 3DOF has been researched and the various simulation and experiments verified the performance of the system. The system is composed of two sides facing with each other, each with one or two lasers, a 2-DOF manipulator, a camera, and a screen. The 6-DOF displacement is calculated from the positions of the projected laser beams and the rotation angles of the manipulators on both sides by using iterative method such as extended Kalman filter (EKF) or Newton-Raphson. Since the computation time is relatively long due to the multiple iterations, this paper proposes non-iterative novel incremental displacement estimation (IDE) method that updates the displacement by using the previously estimated displacement and the difference of the previous and the current observed data. To verify the performance of the proposed method, a simulation has been performed and the result shows that the proposed non-iterative method estimates the displacement with the same level of accuracy in significantly reduced computation time compared to the EKF with multiple iterations.