Metal-free catalysts with controllable compositions are quite attractive for ORR/OER applications in fuel cells due to their low cost, high stability and high efficiency. Nitrogen-doped graphdiynes have recently emerged as such a promising metal-free ORR catalyst, with excellent catalytic performances compatible to Pt/C. Considering the mechanism of their outstanding activities, the debate still goes on whether the sp-hybridized or pyridinic nitrogen dopants paly the crucial role. Moreover, will other heteroatoms doping into graphdiynes lead to the enhanced ORR/OER activity? To solve the debate and answer the question, we studied the electrocatalytic activities of X-doped graphdiynes (X = B, N, P, S) toward ORR/OER by means of density functional theory (DFT) computations. In total, 15 models were constructed for X-doped graphdiynes, including one for pristine graphdiyne (Gdy), five for N-doped graphdiynes, and three for each B-, P- and S-doped graphdiynes. We revealed that the sp-N-doped graphdiyne, the graphitic S-doped and the graphitic P-doped graphdiyne exhibit comparable or even better catalytic activities compared with Pt/C (η = 0.44 V) or RuO₂ (the most active OER catalyst so far, η = 0.37 V). Among N-doped graphdiynes, the sp-N-doped graphdiyne is most active for both ORR (η = 0.49 V) and OER (η = 0.40 V), respectively. Among all heteroatom (B, N, P and S) doped graphdiynes, the graphitic S-doped graphdiyne is the best ORR catalyst (η = 0.42 V), while the graphitic P-doped graphdiyne is the best OER catalyst (η = 0.35 V). This study not only gains deep insights into the catalytic activity of N-doped graphdiyne for ORR, but also guides the developing of graphdiyne-based catalysts beyond N doping.