The invention includes a FeNiCo magnetically soft alloy and a production method thereof, wherein the FeNiCo magnetically soft alloy has high magnetic induction intensity, high magnetic permeability, low coercive force, high stability and good corrosion resistance in a low magnetic field. The FeNiCo magnetically soft alloy comprises the following components by mass percent: not more than 0.02 percent of C, 0.2-0.80 percent of Si, not more than 0.50 percent of Mn, 29.00-35.00 percent of Ni, 25.00-32.00 percent of Co, not more than 5.00 percent of Mo, not more than 0.50 percent of Cu, 0.01-0.55 percent of microelements including 0.001-0.05 percent of rare earth elements, and the balance of Fe and inevitable impurities. The FeNiCo magnetically soft alloy is processed and manufactured by adopting the methods of vacuum melting, forging, hot rolling and cold rolling, and after heat treatment, the FeNiCo magnetically soft alloy has the characteristics of high magnetic induction intensity, high magnetic permeability, low coercive force, high stability and good corrosion resistance in a low magnetic field, and can be manufactured into the transducer, the filter, the electromagnetic valve, the transformer and the like in the field of aviation, aerospace, navigation, electron, electric power and the like.