We theoretically demonstrate the influence of dark states on single-mode, and two-mode optical squeezing in a four-level atomic-cavity coupling system through fifth- and third-order cascade nonlinearity. We first show the cone emissions of self-diffraction, and phase-conjugate spontaneous parametric (SP) four-wave mixing processes. And then, we inject coherent or Einstein-Podolsky-Rosen field into the SP-MWM channels to investigate the corresponding squeezing. The investigations have potential applications in quantum information processing.