When encountering complex formations during drilling operations, the drilling fluid flow rate ranges from 0.3 to 1.1 m3/min, which is below the applicable flow rate range of the existing continuous wave mud pulse tool (1.0–1.7 m3/min). Hence, it is necessary to design new pulse tools with lower flow rates to meet the requirements of drilling in complex reservoirs. The present study uses the pressure drop (1.42–4.92 MPa) of the conventional 675-type pulse tool as a reference. Based on the principle of pressure drop equivalence, the design of the fixed rotor port number and fixed rotor clearance for low-flow pulsers is conducted. A pressure drop chart for low-flow pulsers is drawn, and the rationality of the design is validated through numerical simulation analysis. In low flow rates, the maximum flow rate is 3.7 times the minimum flow rate. A single design could not meet the required range of flow rates, so three different designs were developed: 2-disc, 3-disc, and 4-disc configurations, as well as four the dimensions of axial gap of 1.2, 1.4, 1.6, and 1.8 mm. The 2-disc, 3-disc, and 4-disc pulse tool were designed for flow rates of 0.3–0.5 m3/min, 0.5–0.8 m3/min, and 0.6–1.1 m3/min respectively; amplitude ranges were 1.38–3.84 MPa, 1.31–3.42 MPa, and 1.14–4.82 MPa, all of which are comparable to the pressure wave amplitude range of a conventional 675-type pulse tool. Numerical simulation analysis shows that the equivalent pressure drop is slightly higher than the actual pressure drop under different flow rates, with a deviation of about 20%. In low flow rates, continuous wave transmission attenuates more slowly, and the signal strength at the same transmission distance is comparable to that of a conventional flow rate pulsator. The paper proposes a design principle based on the equivalence of pressure drop ranges, offering a novel approach for the structural design of low-flow pulse tools. This lays a theoretical foundation for the utilization and optimization of pulse tool under low-flow conditions. This paper presents a novel approach for the structural design of low-flow pulse tool, providing a strong technical foundation for rotary steering under complex formation conditions.