The invention relates to a method to extract cobalt from primary alloy of nickel-copper by using carbonyl. The process of extracting is characterized in that: Under the pressure of 20.0-25.0MPa and the temperature of 150-250deg.C, the primary alloy of nickel-copper carries carbonylation reaction by continuously inletting CO with catalyst. In this method, the reaction temperature for composing cobalt carbonyl is low and has extensive applicability and ideal effect. The yield of composing cobalt carbonyl is high and the reaction time is short. Because of being under high pressure, requirements of reaction materials are not exacting, which makes its extensively application. With its simple crafts and flush materials, the method is applicable for commercial production.