Abstract: High-performance infrared detectors—particularly long-wave infrared (LWIR) HgCdTe detectors—require lower temperatures to suppress intrinsic thermal noise, thereby enhancing the signal-to-noise ratio and detection sensitivity. For space telescopes, satellite reconnaissance, and precision-guided systems that demand extremely high imaging stability, the low-vibration characteristics of 30 K pulse tube cryocooler are of critical importance. Traditionally, two-stage pulse tube cryocoolers have been employed to achieve cooling power at 30 K. However, such two-stage configurations introduce structural complexity and additional weight. Therefore, the development of a single-stage, high-efficiency 30 K pulse tube cryocooler is of great significance for improving the performance and integration of spaceborne long-wave infrared detectors. In this study, we developed a single-stage coaxial pulse tube cryocooler and systematically investigated the effects of the inertance tube and operating frequency on its cooling performance. In numerical calculations, it was found that the increase in inertance tube length can increase the phase difference between the mass flow and the pressure in the whole refrigerator, and the increase in frequency can also bring about a similar increase. This shows that by adjusting the inertance tube and frequency at the same time, the phase in the refrigerator can be made appropriate, and the whole machine can also be made to work at a frequency with higher efficiency and less loss. Additionally, double inlet configuration was adopted to further reduce the no load temperature. With an input electrical power of 150 W, the PTC delivered a cooling capacity of 1.2 W at 30 K or 2.3 W at 40 K, corresponding to relative Carnot efficiencies of 7.0% and 9.7%, respectively.