This paper presented a fundamental investigation on the formation mechanism and compatibility of microstructure/mechanical property of Fe-Cr-Ni-B steel samples, which were built by the divided-area forming and integral connection methods. Results indicate that the stress at the edge of the specimen produced in additive manufacturing is reduced by the divided-area forming and integral connection method. According to the microstructure analysis using stereology microscopy/optical microscopy/scanning electron microscope/X-ray diffractometer/Schaeffler diagram, the macrostructure is distributed in strip band geometry and the microstructures consist of dendrites with the intermetallic phases containing austenite phase, boride/matrix eutectic phase. Additionally, the macrostructure strips near the bonding line bend to the building direction and are discontinuous because of the unique forming method. However, the microstructures and composition of the samples are homogeneous. Due to the existence of boride and the finer microstructures, mechanical properties analysis shows that the alloy has high hardness, high ultimate strength and bad deformability. The hardness distribution is homogeneous apart from some positions of the re-melting zone and the heat-affected zone near the bonding line, which have a relatively lower hardness because of differences in microstructure.