The existing multi-baseline methods have some problems of low accuracy and intensive calculation. In order to solve the problems, a new multi-baseline InSAR elevation inversion method based on a rigorous geometric model instead of a simplified model is proposed in the letter. This method introduces the three-dimensional reconstruction model based on rigorous geometric model and the unknown full cycles of interferometric phase as a parameter to iteratively solve the 3-D coordinates of the target. With adopting the 3-D coordinate information of targets to connect different interferometric data, the new method obviously weakens the effects of system errors on solving the integer cycle and is more reliable than conventional multi-baseline InSAR methods. The experimental results show that the speed and accuracy of the new method are better than the existing methods.