3D lung information can help doctors making faster and more accurate diagnosis. However, 3D lung reconstruction is derived from stacking of two-dimensional tomographic images. The quantity of two-dimensional images restricts the quality of 3D reconstruction. Increasing the number of electrode layers could achieve more two-dimensional images. However, the calculation complexity is increased and imaging speed is down. The inter-layer interpolation can solve this problem, however, the specificity and irregularity of human body geometry make electrical impedance tomography (EIT) lung images irregular. As a result, the traditional interpolation algorithm suitable only for regular images which cannot be directly applied to EIT images. Thus, a three-dimensional interlayer interpolation algorithm suitable for pulmonary electrical impedance is proposed. Firstly, the contour of the interpolated image is obtained, and then the pixel value is interpolated with the corresponding point. Simulation and experiment verify that the relative error of the new interpolation algorithm is 5. 69%, 3. 3% lower than that of linear interpolation and spline interpolation respectively. The three-dimensional interpolation method based on contour shape can further improve the quality of three-dimensional electrical impedance imaging and better reflect the real shape of the lung under the condition of limited measurement data.