Hi wanglijun,
Have you refer the qspi_external_flash_s32k148 in S32SDK S32K1xx RTM v3.0.0 Example Projects?

If you are using S32K148EVB, are you measure the QSPI_A_SCK at pin6 of U508?

Have you change the hardware according to the description of External Flash over QuadSPI?

Can you describe the configuration in detail? Maybe you can screenshot your configuration of clock and QSPI.
Best Regards,
Robin