An improved touch-trigger probe method for surface parallelism measurement is proposed, which enables conventional mechanical probe-based detection techniques to evaluate the surface parallelism degree with higher accuracy. The distance detection of the sensing probe is equipped with a simple optical arrangement associated with the digital image correlation method to perform submicron accuracy measurements. The optical arrangement consists only of an inexpensive USB digital microscope. A feasibility study of the measurement method was carried out by measuring three gauge blocks with known parallelism deviations. The experimental setup for the measurement of parallelism error of gauge blocks is described in detail. The experimental results using the proposed method are in good agreement with those certified by the supplier. It has been confirmed that the final accuracy of the developed system could be able to reach the submicron level and meet the requirement of the metrology. In addition, this system is simple to manufacture, low in cost, and easy to operate.