AbstractTesla turbines, featuring bladeless turbomachinery and energy transformation using the viscosity of the working medium, have wide application prospects in renewable energy utilization as micropower equipment and portable power units and show better aerodynamic performance with a smaller turbine size. In this paper, a miniaturization method of Tesla turbines, including the stator and rotor, was proposed based on its sensitivity analysis results and flow similitude law. A typical Tesla turbine with a disc outer diameter of 100 mm was miniaturized to 50, 20, and 10 mm, respectively. In addition, the miniaturized Tesla turbines, including both the simplified single‐channel turbine model and the multichannel turbine model used in practical applications, were simulated numerically. The results show that the miniaturization method that maintains the two high‐impact dimensionless parameters at their optimal values is simple, reasonable, and effective. The isentropic efficiency of the single‐channel Tesla turbine decreases slightly with its scaling down. However, for the multichannel Tesla turbine in practical applications, the isentropic efficiency increases significantly with a decrease in turbine size, due to a decrease in the impact of the outermost disc channel on the flow fields of the inner disc channels (called the casing wall effect). This is embodied by the phenomenon that part of the working medium in the inner disc channels flows into the outermost disc channel through the nozzle‐rotor chamber, and the proportion of this part of the working medium decreases significantly with a decrease in turbine size. In conclusion, the Tesla turbine with a smaller turbine size exhibits better aerodynamic performance and has great potential in the field of microturbomachinery.