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