Abstract: In this paper, the development of calibration of ultrasensitive leak detection in the world is reviewed. The ultrasensitive leak detector is a significant tool for packaging high reliability and long-life vacuum devices, at present, the reported lower limit of that can reach 10⁻¹⁶ Pa·m³/s. However, the correctness of leak detection results is the key factor for device reliability, which mainly depends on the performance and calibration of the leak detector. The standard leak, the platinum wire leak with variable leak rates and the standard gas flowmeter have been used as reference standards to improve the correctness of leak detection results for long years all over the world. The method of the standard leak is to use the leak with the current lower limit of only 10⁻¹¹ Pa·m³/s as the reference standard. Due to the deviation of the leak itself and the linear recurrence method of mass spectrometer spanning several orders of magnitude, the deviation of the leak detection results in the range of less than 10⁻¹⁴ Pa·m³/s can reach one order of magnitude. Using the platinum wire leak as the reference standard can provide variable leak rates in the range of (10⁻¹⁰～10⁻¹²) Pa·m³/s, and the leak detection results will be more accurate compared with the standard leak method. In recent years, the newly developed standard gas flowmeter with a lower limit of 10⁻¹⁶ Pa·m³/s solves the calibration problem of the ultrasensitive leak detector in the whole measurement range, reducing the combined standard uncertainty of the leak detection results to less than 15%, and improving the reliability of long-life vacuum devices.