In the design of molecular organic nonlinear optical (NLO) chalcone crystals, how to balance the stability of the crystal structure and the π-conjugation length while enhancing the NLO activity of the chromophore remains a challenge. In this study, we have synthesized a series of crystals 6MNPP (C20H16O2, Pca21), 6MN4TP (C21H18O2, Pca21), 6MN4EP (C22H20O2, Pca21), and 6MN3TP (C21H18O2, P21) by adding a benzene ring in D−π–A−π–D structure design and introducing new functional groups with large differences in electron-donating ability at both ends of the molecule. All four crystals are non-centrosymmetric structures, and the identification of NLO activity has been well demonstrated by analysis and characterization. Remarkably, 6MNPP crystals are competitive with similar NLO chalcone crystals, mainly including a higher second harmonic generation efficiency (9 × KDP) and higher melting point (Tm = 151.6 °C). Furthermore, first-principles calculations show that the second-order NLO coefficient d15 = 7.843 pm/V, at1064 nm. All the results suggest that 6MNPP crystals have significance potential in the NLO applications.