The objective of work proposed in this paper is to propose a new method of measuring gas leakage for pneumatic industry. Compared with traditional flow measurements, equipment using this method can be connected to the pipeline in parallel. The measurement is enabled by employing a standard flow. Standard flow is used to determine the internal volume of the measured equipment. An algorithm is formulated to describe, to the extent possible, the relationship between gas leakage and standard flow. This paper also proposes a pressure differentiator that contains a slit-type laminar flow element. The measurement deviates from the theoretical leakage values by less than 5%, and shows a good precision and scope. In addition, the proposed parallel connection based on standard flow makes easy operation and fast measuring possible, thus promising new area of application for pneumatic equipments.