Abstract: In order to investigate the thermal hydraulic characteristics of the steam generator heated bilaterally during steady state and transient process, a mathematical model to formulate the physical phenomena in the steam generator is established. It is a one-dimension, homogenous flow model. According to the established model, the code to predict the thermal hydraulics characteristics of steam generator was developed. It can calculate the steady state and transient enthalpy fields, temperature fields of primary coolant and secondary fluid, wall temperature of inner and outer tube etc. The calculation results are analyzed and the results have important meanings to the structure design， steady-state and transient state safe operation of steam generator.