Abstract: This paper introduces a calibration method for mask particle filtration efficiency testers, employing an in-situ aerosol dilutor as a standard device. This novel approach aims to address the limitations of operability and traceability inherent in traditional calibration methods such as standard photometers and filter membrane techniques. Characterized by a combination of multiple flow-limiting capillaries and in-situ aerosol dilution, the in-situ aerosol dilutor is designed to fit and function at the mask fixture position. When operating at a known flow rate, the calibrated dilutor calculates its dilution ratio based on the differential pressure data gathered during calibration. The article further discusses the calibration method for the dilution ratio, asserting that this ratio can be directly converted to a reference value for the dilutor's filtration efficiency. The calibration process is compared to coaxial non-uniform aerosol particle sampling, with a derived calculation of the Stokes number showing that the capillary suction efficiency is near 1. Additionally, the transport efficiency in the capillaries, accounting for diffusion loss, is calculated to be over 0.99. Calibration experiments were conducted with the in-situ aerosol dilutor on typical measurement objects, accompanied by an uncertainty analysis of the reference values. Collectively, these findings substantiate the feasibility and effectiveness of the dilution method calibration.