Background <p>Finite element analysis (FEA), digital image correlation (DIC), and strain gauge are usually used for test monitoring. Reconstructed by FEA strain field and strain gauges, the fusion field (DT-SFRM) has higher accuracy than FEA, and DT-SFRM accuracy is acceptable for small structural deformation. However, large deformation of thin-walled structures is accompanied by complex strain field, and the difference in strain distribution between FEA and strain gauges data increases sharply. The low-accuracy FEA strain field and small amount of strain gauges lead to insufficient accuracy of DT-SFRM.</p> Objective <p>This study aims to construct a high-accuracy strain field for test monitoring.</p> Methods <p>A strain field reconstruction method based on digital twin (DT) by multi-level fusion of multi-type data (DT-MFMD) is proposed. Large number of relatively high-accuracy DIC data is used to improve global FEA strain field accuracy. The high-accuracy strain gauges are used to further improve fusion field accuracy of FEA and DIC. A tensile test of large opening plate shell (LOPS) is performed to verify the advantage of DT-MFMD.</p> Results <p>The AvgErr (6.6%) and MaxErr (23.5%) of DT-MFMD are 16.0% and 58.8% lower than those of DT-SFRM, and the DT-MFMD is less affected by large deformation. In addition, the strain gauges number of DT-MFMD reduces by more than 62.5% under the same accuracy goal compared with that of DT-SFRM.</p> Conclusions <p>The DT-MFMD is validated to have a better application prospect for large deformation and complex strain field distribution.</p>