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The multiport hybrid molecular pump is a new type of molecular pump that was specifically designed for use in helium mass spectrometer leak detectors. This pump enables the instrument to detect both downstream and counter-current leaks. Access to different extraction ports can fulfill various leak detection requirements, which broadens the application range of these detectors and improves their detection efficiency. This paper establishes a model for the calculation of the parameters of a helium mass spectrometer leak detector under fine inspection conditions, studies the influence of different turbine blade parameters and fine inspection port positions on pumping performance and leak detection, discusses a method to determine turbine blade parameters and fine inspection port positions under fine inspection conditions, and provides a theoretical basis for the development of helium mass spectrometer leak detection technology and the optimization of multiport hybrid molecular pump structures. The results show that reducing the blade inclination and increasing the number and height of blades can improve the detection sensitivity. Provided that the hybrid molecular pump has good pumping capacity, the helium mass spectrometer leak detector can obtain high detection sensitivity when the single blade inclination angle is 25°, the number of turbine blades is 25 to 30, the blade height is 3 mm, and the blade thickness is 0.6 mm to 0.8 mm. To determine the position of the inspection port, it is necessary to consider the actual requirements of the leak detector, such as the working pressure of the inspected parts, the leakage rate and the minimum detectable leakage rate. When the inspection port is between the 7th- and 8th-stage blade rows, optimum working pressure of the mass spectrometer chamber for better leak detection performance and large pressure detection range are guaranteed. Full article