The plasmon cavity system formed by the scanning tunneling microscope tip and substrate has attracted much attention due to its ability to break through the diffraction limit, enhance the electromagnetic field by hundreds of times, and localize it at the nanometer or even sub-nanometer scale. The plasmon cavity system formed by the scanning tunneling microscope tip and substrate can serve as an advanced platform for studying superradiance phenomena at the ultrafast scale. Methylene blue molecules have a wide range of applications in the field of optics due to their significant light absorption and fluorescence emission characteristics. This article applies macroscopic quantum electrodynamics and open quantum system theory to explore the radiation dynamics of methylene blue molecular clusters with three different configurations: cyclic, two-dimensional planar, and one-dimensional chain, in specific scanning tunneling microscope nanocavity and picocavity. Taking the cyclic molecular clusters as an example, the radiation effects of different external field excitations on the molecular clusters in the cavity are studied. The research results indicate that for the same molecular cluster configuration, the scanning tunneling microscope picocavity has a more significant superradiance intensity, while the scanning tunneling microscope nanocavity has a longer duration of superradiance. From the perspective of symmetry, one-dimensional chain molecular clusters only have axial symmetry, while two-dimensional planar and cyclic molecular clusters have both axial symmetry and central symmetry. Cyclic molecular clusters also have multiple rotational symmetries, so in the same scanning tunneling microscope cavity, the higher the arrangement symmetry of molecular clusters, the easier it is to generate obvious superradiance pulses. In addition, the scanning tunneling microscope picocavity is more sensitive to changes in external conditions such as excitation wavelength due to its higher spatial resolution and stronger local field enhancement effect. These results indicate that by designing the cavity structure and geometric configuration of molecular clusters reasonably, the occurrence and enhancement of superradiance phenomena can be effectively controlled, and the time scale of superradiance pulses can be extended to the picosecond level, providing new ideas and methods for future practical applications in the fields of optics and nanotechnology.