Designing low-cost, highly efficient, and durable electrocatalysts for carbon dioxide reduction reaction (eCO2RR) to value-added chemicals is an appealing approach to balance the global carbon emission. Heterogeneous molecular catalysts is emerging as an important area for CO2 utilization. Herein, a series of atomically isolated transition metal-N4 sites anchored on porphyrin framework (TM/PRF) molecular catalysts are employed as electrocatalysts for eCO2RR because of their well-defined structure, the versatility and relatively low cost, and remarkable activity, which allow the establishment of precise structural model for a better understanding of the CO2 reduction mechanism. Based on density functional theory calculations and the computational hydrogen electrode model on 27 candidates, we propose a number of TM/PRF (TMs = Ni, Co, Mn, Cu, Ag, Au, Zn, Pd, Ti, V, Cr, Ta, W), which show promise of highly active and selective catalysts for carbon monoxide, formic acid, methane and methanol production, while simultaneously suppress competing hydrogen evolution reaction. Studies have shown that the TM center plays a crucial role in determining the catalytic performance of the material. And the TM/PRF molecule tends to stabilize different radical intermediates at the TM site. Thus, when reacted with a greater number of electrons, highly reduced products are formed. Among the different TM/PRF materials, Ta/PRF and W/PRF have been shown to produce CH3OH selectively at low overpotentials (0.39 and 0.58 V), whereas Ti/PRF has been found as highly selective toward CH4 production with low overpotential of 0.58 V, outperforming most known electrodes. The calulation of activation energy and the d-band center reveal that Cr/PRF shows higher catalystic activity in comparison with other TM/PRF. The advantages of the outstanding selectivity of products, the reduced overpotentials and the higher activity of catalyst allow these new systems TM/PRF (TMs = Ta, W, Ti, Cr) to be promising catalysts, which will motivate more fundamental mechanism studies and technological applications for eCO2RR.