This study investigated the influence of the geometry of the draft tube on the mass transfer and energy efficiency in the airlift reactor with helical sieve plate (ALR-HSP). The power consumption efficiency was 46%-53% higher than the control condition by optimizing the draft tube. A set of empirical equations was used to describe the gas holdup and volumetric mass transfer coefficients corresponding to the geometry of draft tubes in the ALR-HSP for the water-air system. The comparative cultivation of Pichia pastoris was carried out using the ALR-HSP and the conventional airlift reactor (CALR). The biomass increased by 20%, the maximal specific growth rate during the logarithmic growth phase nearly doubled, and volumetric oxygen transfer coefficient increased by 21%-47% under the same culture conditions. Results preliminarily demonstrated the superior performance and practicability of the ALR-HSP in enhancing oxygen transfer efficiency and aerobic biological reaction efficiency. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.