Hi @Jennifer Yan,
The PS_SRST_B is present to allow the Xilinx Tools to reset the processor during debug operations through the dedicated pin on the Zynq processor: https://digilent.com/reference/programmers/jtag-hs3/reference-manual#xilinx_zynq-7000_and_soc_support. Xilinx provides a bit more information about this pin here: https://docs.xilinx.com/r/en-US/ug585-zynq-7000-SoC-TRM/External-System-Reset-PS_SRST_B.
If you are not using a Zynq device, then you can leave this pin as a no-connect or implement a weak pull-up, 100k ohm, to keep it from floating.
Let me know if you have any questions.
Thanks,
JColvin
