Single layer blue phosphorus (SLBP) is a promising two dimensional material for nano electronic devices, but the electronic structure and hydrogen storage property of modified SLBP received little attention. Li atoms can be strongly bonded on SLBP in a 1:1 Li/P ratio with a binding energy larger than the cohesive energy of bulk Li. The geometric structure of SLBP suggests the 3s3p orbitals of the P atom hybridize in sp(3) manner. But our analyses show that the 3s and 3p orbitals form bonding and antibonding orbitals respectively. The 3s orbitals are fully occupied as they have much lower energies, and the bonding orbitals formed by P 3p are occupied in pure SLBP. The decorated Li atoms transfer their 2s electrons to the antibonding orbital formed by P 3p. The Li atoms exist as +1 cations and they are ionically bonded on SLBP. H-2 molecules adsorbed on the Li+ cations are strongly polarized and form strong adsorption. When two H-2 are adsorbed on each Li atom decorated at the 1:1 Li/P ratio, the hydrogen storage capacity reaches 9.52 wt% but the H-2 molecules are arranged in two layers with the adsorption energy 0.168 eV/H-2. When the Li atoms are decorated alternatively on the two sides of the P-6 rings with a Li/P ratio of 1:2, each Li atom can absorb two H2 molecules in a single layer; the hydrogen storage capacity is 5.48 wt% and the adsorption energy reaches 0.227 eV/H-2. These results mean the Li decorated SLBP can work at ambient temperature with high reversible hydrogen storage capacity. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.