[grub 2.02 help] not a valid root device

[????]

hi!
i have a problem:
when i start up the grub 2.02,my usb device are identified as efi 
device:(hd1,msdos1); At this time,i chainloader ,it is correct,and the winPE 
system can be started up!

Then i use the command [nativedisk] to drive it to usb,then the usb device 
drived as usb SCSI device:(usb0a,msdos1);
The question is: at this time when i chainloader ,it is not correct, and 
tip[not a valid root device].

How to solve this problem? or how can i drive my usb device again to efi device?
Thanks very much!