Two-dimensional obstructed atomic insulators with fractional corner charge in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mrow><mml:mi>M</mml:mi><mml:mi>A</mml:mi></mml:mrow><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>Z</mml:mi><mml:mn>4</mml:mn></mml:msub></mml:mrow></mml:math> family

According to topological quantum chemistry (TQC), a class of electronic materials has been called obstructed atomic insulators (OAIs), in which portion valence electrons necessarily have their centers located on some empty Wyckoff positions (WPs) without atom occupation the lattice. The obstruction centering these coinciding with host atoms is nontrivial and results metallic boundary states when properly cut. Here, basis first-principles calculations combination TQC analysis, we propose two-dimensional ${MA}_{2}{Z}_{4}$ $(M=\mathrm{Cr}, \mathrm{Mo}, \mathrm{W}; A=\mathrm{Si} \mathrm{and} \mathrm{Ge}; Z=\mathrm{N}, \mathrm{P}, \mathrm{As})$ monolayers are all OAIs. A typical case recently synthesized ${\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ (${\ensuremath{\alpha}}_{1}\text{\ensuremath{-}}{\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$). Although both ${\ensuremath{\alpha}}_{1}$- ${\ensuremath{\alpha}}_{2}\text{\ensuremath{-}}{\mathrm{MoSi}}_{2}{\mathrm{N}}_{4}$ trivial insulators, it WPs in-gap corner at three vertices triangle-shaped nanodisk samples respecting ${C}_{3}$ rotation symmetry, can be explained by filling anomaly electrons. In addition, monolayer exhibits unique OAI-induced edge along $(1\overline{1})$ edge. readily quite stable large bulk bandgap 1.94 eV, makes identification most possible for experimental clarification.