The invention discloses a granular iron preparation system and method. The granular iron preparation system comprises a slag melting device, a granulator, a reduction roasting device, a magnetic separation device and a gravity concentration device. By the system, melted copper slags are taken as raw materials, the problem that the traditional high-temperature copper slags only can be continued being treated after being cooled by water quenching or cooled slowly is solved, high-grade granular iron and zinc oxide dust can be prepared, and the heat utilization rate of the system is high. In addition, an additive inlet is formed in the slag melting device, an additive is added in the high-temperature melted copper slags before heating treatment, the melted copper slags can be homogenized after being stirred by a stirrer, the interior structures and chemical components of the copper slags are adjusted directly, the metallurgical performance of the copper slags is improved, then the copper slags are granulated at high temperature, so that granulated copper slag raw materials can be provided for direct reduction of a rotary hearth furnace, technologies such as pelletizing, drying and pellet preheating are omitted, the reduction time of the rotary hearth furnace is shortened, and the energy consumption of the rotary hearth furnace is reduced.