This study is related to consequence analyses of accidental natural gas explosions and used to assess the risk of the long-distance transmission pipeline system. In these consequence analyses, it is indispensable to adequately predict the blast wave propagation of gas vapor cloud explosions (VCEs) in open space. In this study, a new theoretical prediction method for natural gas VCEs in open space was developed and a full-scale experiment involving explosion in a natural gas pipeline was carried out. The predictions by the improved theoretical method agreed well with the results of the full-scale experiment. On the basis of damage criteria, to demonstrate the probability and potential damage range to humans and surroundings, risk analysis of this case was performed on the PHAST simulator. We conclude that a nearly 100% fatality is expected in a blast wave zone of within 160 m, while the explosions made serious effects on the surrounding construction, causing all of the buildings to collapse with the radial distance of 156 m. Relatively, there is no harm when people stay beyond the ellipse diameter of 545 m, and no damage to the surrounding buildings beyond the radial distance of 1755 m.