The headlight assembly line for H4 halogen bulbs automatically combines the halogen capsule bulb, metal cap, bulb holder, and prefocus base to form H4 halogen bulbs. This assembly line is characterized by high automation and is capable of inspecting the products in-real time. This line features headlight bulb alignment machines for adjusting focus and installing, as well as the optional headlight bulb adjusting machine and headlight bulb specification data inspecting machine following customer needs.