The present invention relates to a field emission light source device, which includes: a base substrate; at least one cathode strip, disposed over the base substrate; at least one emissive protrusion, disposed over the cathode strip and electrically connected to the cathode strip; an insulating layer, disposed over the cathode strip and having at least one opening to allow the emissive protrusion to protrude out of the opening; at least one anode strip, disposed over the insulating layer, where the cathode strip and the anode strip are arranged into an m×n matrix and the at least one anode strip individually has an impacted surface corresponding to the emissive protrude; and a phosphor layer disposed over the impacted surface. Accordingly, the present invention can enhance light utilization efficiency of a field emission light source device.