The invention provides a method for automatically measuring a plurality of blades of an integral impeller and a special indexing device thereof. The method comprises the following steps: (1) measurement planning on a first blade is performed on a CAD data model to generate a DMIS file; (2) an integral impeller is clamped on the indexing device designed in the invention, and an integral impeller work piece coordinate system is positioned; (3) the axis direction of the device is measured, eccentricity compensation is calculated, and DMIS files of other blades are generated; (4) the first blade is measured by the use of the DMIS file thereof; (5) a measuring device is started to rotate the other blades to the position of the first blade, and measurement is carried out by the use of the DMIS files of the blades until measurement on all the blades is completed; and (6) measurement results are processed and measurement data of the blades is obtained. By adopting the measuring method of the invention, automatic measurement on the plurality of blades of the integral impeller can be realized, deviation between the axis of the measuring device and the central axis of the integral impeller can be eliminated, and the measuring precision is high.