The UV-Vis absorption spectra of the discrete magnetic molecules [py.H]3[FeBr4]2Br were calculated based on density functional theory with B3LYP exchange-correlation functional in acetonitrile solution. The molecule was dissolved dilutely in acetonitrile to ensure that its experimental response can be attributed to a single dispersed molecule without significant interaction to other molecules. The experimental UV-Vis absorption spectra show four typical peaks in UV region and three peaks in visible region. A number of different basis sets are employed to compare the experimental data with the theoretical absorption spectra on different levels of basis sets. The comparison of experimental data with theoretical computation shows that choosing 6-311++G** improves computational results mainly in visible region and makes little differences between results based on DFT and TDDFT in other wavelength domains, especially in UV wavelengths. The simulated results are of importance in simulating the response of these molecular magnets as a discrete asymmetric unit to applied light.