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In this study,D → P(π,K)helicity form factors(HFFs)are investigated by applying the QCD light-cone sum rule(LCSR)approach.The calculation accuracy is up to the next-to-leading order(NLO)gluon radiation correc-tion of twist-(2,3)distribution amplitude.The resultant HFFs at a large recoil point are Pπt,0(0)= 0.688+0.020-0.024 and PKt,0(0)= 0.780+0.024-0.029,in which the contributions from the three particles of the leading order(LO)are so small that they can be safely neglected.The maximal contribution of the NLO gluon radiation correction for Pπ,Kt,0(0)is less than 3％.After extrapolating the LCSR predictions for these HFFs to the whole q2-region,we obtain the decay widths for semileptonic decay processes D → Plυl,which are consistent with the BES-Ⅲ collaboration predictions within error limits.After considering the D+/D0-meson lifetime,we give the branching fractions of D → Plυl with l = e,μ;our predictions also agree with the BES-Ⅲ collaboration results within error limits,especially for the D → πlυl decay process.Finally,we present the forward-backward asymmetry AlFB(q2)and lepton convexity parameter ClF(q2),and further calculate the mean value of these two observations,and,which may provide a way to test those HFFs in future experiments.