Abstract: The present invention discloses a novel phosphodiesterase 4 (PDE4) inhibitor ZL-n-91 for applications in preparing drugs for treating proliferation and metastasis of prostate cancer. The animal experiments and cytological experiments in mice showed that the PDE4 inhibitor ZL-n-91 of the present invention can significantly inhibit the proliferation and metastasis of prostate cancer cells, indicating that the PDE4 inhibitor ZL-n-91 is expected to be an important target for treating proliferation and metastasis of prostate cancer. It will lay a foundation for preparing drugs against proliferation and metastasis of prostate cancer, presenting good prospect for development and application.