In view of actual environment of carbon nanotubes-field emission display, the electric field and electric potential distribution of single vertical carbon nanotube, including 45o with the same length of the vertical one and 45o with the same height, are calculated respectively. The results indicate that the electric field intensity's ratio for the three types of carbon nanotubes is about 13 : 10 : 12. The further analysis shows that if the uniformity of field emission is desired to obtain improvement, the height of inclining carbon nanotubes should be increased on condition that the vertical and inclining carbon nanotubes exist simultaneously in the cathode of field emission display.