Abstract: A variable density model with exponential density contrast is used for inverting Moho depths instead of constant density model.The method is introduced and some formulae are derived.The Moho depths of Qinghai-Tibet plateau are inversed from gravity data with exponential density model.The inversion results demonstrate that the Moho depths of Qinghai-Tibet plateau are shallow around the edges,and deep at the center.The gradients at the edges are steeper than at the center.The variable density model is more suitable for inversion with Moho depths structures than constant density model by comparison of Moho depth from seismic inversion.