@zguo in your screen shot you have listed the full path to the boot file, that should only be the boot file name in reference to the /tftpboot directory which for tftp is the root directory for tftp.
I think you have something missing in your setup. You can use the FOG server or a witness (third computer) with wireshark installed to monitor the communications. If you use wireshark you can use a capture filter of port 67 or port 68
Or follow the guide here to use the fog server to monitor the dhcp/pxeboot process. https://forums.fogproject.org/topic/9673/when-dhcp-pxe-booting-process-goes-bad-and-you-have-no-clue then load the output file into wireshark.
So what you are looking for is the DORA process (DISCOVER, OFFER, REQUEST, ACK).
So the pxe booting computer will send out a discover packet (please configure me)
The dhcp server will respond with an OFFER packet that should contain the next-server and boot-file fields as well as dhcp options 66 and 67 which will align with the next-server and boot-file fields. My guess is that there is something wrong with OFFER packet or your dhcp server.