The work aims to improve the microwave absorption performance of carbonyl iron at low frequency and master the method of controlling the frequency of absorption peak. The spherical carbonyl iron was mixed with sheet carbonyl iron to prepare composites. The morphologies of two types of carbonyl iron were analyzed by SEM. The complex permittivity and complex permeability of carbonyl iron composites at different mass ratios (3∶1，2∶1，1∶1，1∶2，1∶3) were measured by vector network analyzer to study the effect of carbonyl iron composites with different morphologies on electro magnetic characteristics and analyze the microwave absorption performance of the composites at different mass ratios. With the increase of the proportion of spherical carbonyl iron, the real imaginary parts of complex permittivity in the composites decreased gradually. The real part of complex permeability in carbonyl iron composites had a small change while the imaginary part decreased. When the mass ratio between the sheet carbonyl iron with spherical carbonyl iron was 1∶2, the minimum reflection loss reached -20.2 dB at 3.08 GHz. The effective absorption bandwidth for RL≤-8 dB reached 2.43 GHz at low frequency. The addition of spherical carbonyl iron into sheet carbonyl iron can control movement of absorption peak at low frequency, improve the microwave absorption within 1~4 GHz and broad the effective absorption bandwidth. The addition of spherical carbonyl iron also decreases the complex permittivity of sheet carbonyl iron, which can make the impedance matching condition better and improve the electromagnetic loss coupling effect, thus enhancing the microwave absorption performance.