Owing to the abundant storage and environmentally benign of Na, Fe, and Mn elements, FeMn-based O3-type NaFe0.5Mn0.5O2 materials were considered to be a promising cathode for sodium-ion batteries. However, the poor rate performance was barely satisfactory to the commercial production. Here, different Na content O3-type NaxFe0.5Mn0.5O2 (x = 1, 0.9, 0.8) for sodium-ion batteries were synthesized by solid-state reaction. The results illustrated that Na-deficient compound was beneficial to improve the rate performance and discharge capacity. Due to the Na-deficient in the octahedral sites, O3-type Na0.8Fe0.5Mn0.5O2 achieved a discharge capacity of 179mAhg(-1) at 0.1 C, which is relatively higher than that of O3-type NaFe0.5Mn0.5O2 (145mAhg(-1)). Besides, the O3-type Na0.8Fe0.5Mn0.5O2 exhibited an initial discharge capacity of 126 mAhg(-1) and outstanding capacity retention of 82.6% after 60 cycles at 1C. The excellent performance indicates that nontoxic and earth-abundant Na-deficient O3-type cathode may be a promising cathode for large-scale application and development of sodium-ion batteries.