This study entailed the development of a high-gradient modulation of microbunching for traditional radiation frequency accelerators using a minimized system driven by a relativistic Laguerre–Gaussian (LG) laser in three-dimensional particle-in-cell (PIC) simulations. It was observed that the LG laser could compress the transverse dimension of the beam to within a 0.7 µm radius ($\text{divergence}\approx 4.3\mathrm{mrad}$), which is considerably lower than the case tuned by a Gaussian laser. In addition, the electron beam could be efficiently modulated to a high degree of bunching effect ($>0.5$) within $\sim 21\mathrm{fs}$ ($\sim 7\mathrm{\mu m}$) in the longitudinal direction. Such a high-gradient density modulation driven by an LG laser for pre-bunched, low-divergence, and stable electron beams provides a potential technology for the system minimization of X-ray free-electron lasers (XFELs) and ultrashort-scale (attosecond) electron diffraction research.