Cosmic rays are one of the important sources of high-energy particles, but at present our understanding of its origin, transmission and interaction process is still very limited. In addition, the exploration of dark matter is also one of the most popular issues in international research. Very Large Area gamma ray Space Telescope (VLAST) is the next generation of flagship space observatory, which has a large acceptance, extremely high angular resolution and energy resolution. It has three sub-detectors, which are anticoincidence detector, silicon tracker and low energy gamma-ray detector and high energy imaging calorimeter, and the last one composed of BGO crystals is the key subdetector. It has 8 layers with 192 crystals per layer, and the size of every crystal is 2.5 cm × 2.5 cm × 120 cm. In order to study the performance of the BGO calorimeter, we carry out the simulation based on GEANT4 software to study energy linearity, resolution, and particle identification ability. In addition, the performance of meter-size BGO crystal produced by Shanghai Institute of Ceramics was tested, the light yield and attenuation length were studied, and the large dynamic range readout scheme with two Avalanche photodiodes (APDs) was also studied. Here, the simulation and experimental test results will be introduced.