As a natural aromatic polymer, lignin has been proven to be a natural broad-spectrum sunscreen agent due to its good UV protection properties. In general, lignin is a complex and heterogeneous macromolecule composed of guaiacyl (G), syringyl (S), and p-hydroxyphenyl (H) units. However, in addition to the three conventional structural units, some unconventional structures such as ferulates, p-coumaric acid, and tricin are also found in gramineous lignins, which leads to considerable impacts on the anti-UV radiation abilities of lignin. Herein six lignin model compounds, including tricin, ferulic acid, p-coumaric acid, sinapic acid, and C5-C5-linked dimers, were designed and applied to investigate the UV protection abilities of typical unconventional structures in straw-like lignin in combination with three different alkali lignins of rice straw, wheat straw, and oat straw. After the addition of different models or alkali lignins to the pure cream or commercial sunscreen, it was found that SPF values of the model-based or lignin-based sunscreens were increased but varied. The highest increase in SPF value was the sample of adding tricin (0.0558 mmol, about 2% by weight) into the low SPF commercial sunscreen, followed by ferulic acid, from 1.06(10.00) to 4.67(38.49) and 3.77(34.69), respectively, displaying the significant increment of the UV protection ability. In contrast, the increments of SPF values after adding p-coumaric acid or sinapic acid into the pure cream or sunscreens were much lower, which reveals, to some extent, the role of methoxy groups in lignin’s UV resistance ability. Considering lignin structural analysis, it was shown that lignin with the high retention of tricin was beneficial to the UV protection effect; meanwhile, the presence of ferulic acid and p-coumaric acid in lignin also significantly impacted the UV radiation resistance of gramineous lignin. Among the three different lignins, alkali lignin with higher tricin content has more apparent advantages as a sunscreen agent, which provides new insights and a theoretical basis for separating gramineous lignin and its following high-value utilization.