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abstract: 'The metallicity and its relationship with other galactic properties is a fundamental probe of the evolution of galaxies. In this work, we select about 750,000 star-forming spatial pixels from 1122 blue galaxies in the MaNGA survey to investigate the global stellar mass – local stellar mass surface density – gas-phase metallicity ($M_*$ – $\Sigma_*$ – $Z$ ) relation. At a fixed $M_*$, the metallicity increases steeply with increasing $\Sigma_*$. Similarly, at a fixed $\Sigma_*$, the metallicity increases strongly with increasing $M_*$ at low mass end, while this trend becomes less obvious at high mass end. We find the metallicity to be more strongly correlated to $\Sigma_*$ than to $M_*$. Furthermore, we construct a tight (0.07 dex scatter) $M_*$ – $\Sigma_*$ – $Z$ relation, which reduces the scatter in the $\Sigma_*$ – $Z$ relation by about 30$\%$ for galaxies with $7.8 < {\rm log}(M_*/M_\odot) < 11.0$, while the reduction of scatter is much weaker for high-mass galaxies. This result suggests that, especially for low-mass galaxies, the $M_*$ – $\Sigma_*$ – $Z$ relation is largely more fundamental than the $M_*$ – $Z$ and $\Sigma_*$ – $Z$ relations, meaning that both $M_*$ and $\Sigma_*$ play important roles in shaping the local 