Biaxially oriented tubular blown film stretching machine by isostatic pressurized water is a simultaneous biaxial stretching process, invented to stretch a high crystalline tubular blown film substrate with heterophasic structure to form a microporous film substrate, especially for microporous polypropylene film. The system comprises sequential sets of variable speed nip rolls, a temperature control water tank, and a water pump unit. The sequential sets of variable speed nip rolls used to stretch the tubular blown film substrate in machine direction, while hot water is pumped and confined inside the tubular blown film substrate creating an isostatic pressure in bubble, lead to an orientation stretching in transverse direction.