A cryo-bulge apparatus, which can be directly installed in the synchrotron radiation x-ray scattering beamline, is designed and manufactured. Using the cryo-bulge apparatus, the crystallization of natural rubber during blowing can be captured in situ. For mechanical measurements, the rubber film is tightly clamped at the periphery of a circular window. A low temperature measurement is achieved by the presence of a large iron block, which ensures low temperature variation (<±2 °C in 1 h) during x-ray data acquisition. Since the incident x-ray beam passes through the top-most position of the rubber film, the information obtained by the current equipment is essentially under an equibiaxial deformation mode. Owing to precisely controlled internal pressure and temperature, the crystallization of rubber can be observed in situ by wide-angle x-ray scattering. The onset of crystallization is observed at a temperature T < 0 °C with an internal pressure P > 21 kPa. This suggests that the crystallization of rubber during blowing can occur under the equibiaxial deformation condition at low temperatures. The power scaling law is found to be 0.52%/kPa. The cryo-bulge apparatus is capable of clarifying the microstructural evolution of rubber during multi-dimensional deformation, which can provide guidance for the optimization of a weather balloon.