An assembly system comprises a fixing device configured to fix a housing and a pressing mechanism adapted to assemble a contact into the housing. The pressing mechanism includes a fixing block having a contact guiding slot adapted to receive the contact therein and a movable block movably mounted on the fixing block and adapted to press the contact downward. The movable block is moved downward to press the contact received in the contact guiding slot into a contact installation slot of the housing in a condition in which the contact guiding slot of the fixing block is aligned with the contact installation slot of the housing.