Unhappy twrp install cm11 zip fail

I plan to upgrade my tf300t to cm11. But now i met some problem

my tf300t is using 4.2.1, and bootloader is ww_epad-110.6.1.27.5

first i unlock the device, then i fastboot twrp v2.6.3.0 in it(I tried several versions, twrp or recovery, but all of those couldn't read internal memory or ext sd card. only this version is ok)

then i wipe data and made it factory reset

finally i choose cm11 to install, and then it told that error flashing zip

and now when i boot the device, it won't go to the android system but go to twrp by itself

what should i do now? should i root it before i install cm11?