Transition metal sulfide pyrite is a kind of excellent photovoltaic material, doping modification is an important mean to improve the properties of pyrite PV. To explore the impact of Co-doped amount on pyrite crystal structure and light absorption performance, nano-micron-sized pyrite samples were prepared via thermal sulfide method at 360 ℃. In addition, the crystal structure, morphology characteristics and grain size of samples were analyzed with X-ray diffraction(XRD)and multi- functional field-emission scanning electron microscope (FESEM). Moreover, the chemical composition of the samples was tested using the energy dispersive spectrometer (EDS), the light absorption performance and the change of the forbidden band width of the samples were characterized through the ultraviolet-visible-near infrared absorption spectroscopy (UV-Vis-NIR). The results of XRD and FESEM indicated that co-doped led to crystallinity changes, crystal grain reunion, larger size in the range of 1～1.45 μm, but did not change the cubic crystal structure of pyrite, compared with pyrite samples without doping. The grain size decreased slightly with the increasing amount of co-doped, but the impact was not obvious. EDS test showed that the actual samples doping was not uneven, the test value was less than the nominal doping Co amount when amount of co-doped was less than 7at%, while it was larger than nominal when doping Co amount was greater than 7 at %.The ratios of S/(Fe+Co) were within the scope of 1.92 to 2.05, the degree of deviation 2 of the ratio suggested the number change of point defect of internal samples, affecting the light absorption performance of the samples. Besides, reflection spectrum showed that band gap Eg was from 0.57 to 0.72 eV. The width of forbidden band reduced (Co3 at%) before it increased as doping Co amount increased (Co5～9 at%). The additional energy level, formed by a number of point defects in internal samples, led to band gap narrowing, as mixing amount of Co increased from 0% to 3 at%. With further increasing mixing amount of Co, S/(Fe+Co) ratio was closer to 2, the crystal structure was more perfect and the Fe vacancy or S clearance point defect ratio was more decreased, leading to the forbidden band width Eg tend to widen. In addition, with the increase mixing amount of Co, the increasing trace CoS2 phase caused the forbidden band width to larger, up to 0.72 eV, as the mixing amount of Co further increased to 9 at %, which was greater than the forbidden band width of 0.65 eV of not doped samples at the same temperature, the same synthetic methods, in theory, which could effectively improve the photoelectric conversion efficiency.