Measuring magnetocrystalline anisotropy field distribution of patterned magnetic nanodots using a microscopically visualizing way is important for understanding some important magnetic behaviors such as switching field distribution (SFD) of patterned recording media. Wepresent a detailed analysis of the remanent domain structures of L1(0)-FePt triangular nanodots as revealed by high resolution magnetic force microscopy (MFM) with the help of micromagnetic simulation, showing that the domain structure diversity can effectively account for a dot-to-dot variation of the magnetocrystalline anisotropy field. Our method could shed light not only on understanding the fundamental causes of a wider SFD but also on designing future nanostructured magnetic devices.