Objective To design a new strain loading device for researching the mechanical biology of adherent cells. Methods Based on the technology of base deformation loading, the controllable and stepper were designed, and the silastic chambers were loaded and the device was provided to realize the cell loading with multiple units and large strain. The device was developed and its loading function were tested. The three-dimensional models of the silastic chamber were established to simulate the loaded chamber by the finite element technology, the uniformity of the strain field were analyzed. The device applied 5% strain to BMSCs with stretch fre-quency at 0.5Hz for 2 hours a day and lasted 5 days, and an inverted phase con-trast microscope was used to observe the morphology of BMSCs. Results The de-veloped device can provide mechanical strain up to 50% for three groups of cells loading substrates with the advantage of large strain, convenient operation and high precision and it could be used for experiments of tension to cells as well as compression, and the frequency of stretch, the time of stretch and strain magnitude could be conveniently adjusted. The tests showed that the strain loading device for adherent cells in vitro was provided with reliable mechanical function, and the de-vice could be operated and observed easily. The finite element method was used to simulate the large deformation of the three-dimensional silastic chambers, and the results of simulation showed that strain was uniform in the area of 60% at the strain of 10%, it could be ensured that the cells were loaded evenly. After the BMSCs were stretched, the morphology of cells were altered, and the BMSCs were flat shaped, and the direction of arrangement tended to be perpendicular to the loading direction of principal strain, which were in good agreement with the literature reports. Conclusions The device has the advantages of reliable operation, wide strain range, adjustable frequency and convenient operation. It can be used to load multiple cell culture substrates at the same time, which provides convenient conditions for the study on cell mechanobiology.