Starting from population density matrix equations, five kinds of nearresonant enhaneed three-photon eleetronic transitions in the interaetion between differently polarized laser fields and molecules with casecade four-level strueture and folding four-level structure are discussed respectively. And ,taking the third transition as the probe signal, the relative intensities and the characteristic of the signals are derived analytically. The line-shape factors and intensity factors of the relative intensities are greater by different degrees when compared with the of three-level molecules.Therefore the relative intensities of the probe signal may be greater by several orders. The Potential applications of these results in moleeular speetroscopic analysis are also diseussed.