The invention relates to a foot-distance-adjustable narrow-base tower steel structure base and a construction method. The steel structure case comprises angle steel trusses, a channel steel bottom plate, upper tower foot plates and lower tower foot plates, wherein each upper tower foot plate is arranged on the channel steel bottom plate; each end part of the lower end of each angle steel truss isconnected with the corresponding lower tower foot plate; one upper tower foot plate is respectively arranged on each end part of the upper end of the corresponding angle steel truss; four parallel strip holes are uniformly distributed in each upper tower foot plate; through the arrangement of the strip holes, the requirement of foot distance change in a certain range is met; the applicability of the base is improved; each upper tower foot plate is connected with a narrow-base tower through screw bolts penetrating through the strip holes; and when an external load is received, each part of thebase jointly acts to resist an external overturning torque and a vertical load. The foot-distance-adjustable narrow-base tower steel structure base provided by the invention is applicable to base construction and pole and tower assembling and erecting projects with the requirement of short construction period and with the constraint that large machinery cannot reach operation sites; and the construction period can be greatly shortened on the premise of ensuring the base design requirements and construction quality.