Cryogenic helium turbine expander is a core component of large helium refrigerators and liquefiers. Two-stage cryogenic helium turbine expanders are designed for 250W@4.5K helium refrigerator. One-dimensional design have been done based on the parameters calculated by the process. According to the geometric parameters calculated by the one-dimensional design, a new modeling method is adopted to design the blade shape of the expander. The two stage turbine expander are successfully applied to firstname.lastname@example.orgK helium refrigerator, and the efficiency of the two expander are higher than 65%.