Fine melt pool (FMP), coarse melt pool (CMP), and heat affected zone (HAZ) are generally observed in the additive manufactured AlSi10Mg alloys. In this study, we demonstrated that the yield strength can be estimated by the combination of the sizes and volume fractions of FMP, CMP, HAZ together with the second-phase hardening. Two different AlSi10Mg alloys fabricated via powder bed fusion (PBF) process were prepared to examine the lattice strain evolution of constituent phases during uniaxial tensile loading via in-situ neutron diffraction measurements. The horizontally-built (Hz-built) exhibited a much better yield and tensile strength as well as elongation compared to the vertically-built (Vt-built) AlSi10Mg alloy. The stress partitioning from Al matrix to reinforcement Si was obtained during plastic deformation regime in both alloys. However, a greater capability of enduring high load of Si and a load transferring back to the ductile Al matrix found in the latter period of plastic deformation are responsible for better tensile properties in the Hz-built AlSi10Mg alloy. We reported empirical strength quantification based on the sizes and ratios of FMP, CMP, and HAZ together with the possible failure mode to prevent early fracture in the additive manufactured alloys.