There exists an optimum soaking time for thermal recovery well. But for super heavy oil which has special properties, agreement in how to determine soaking time has not been achieved. On the basis of energy balance, this study applies non-stabilized well test and mathematical statistical analysis etc to comprehensively determine heat variation values of oil well during steam injection, soaking and production. Heat variation is converted into temperature influence on heated area, which is stacked on temperature field at the end of soaking resulting in actual temperature field in different time of production after well is soaked. Thus the relationship between effective temperature field (determined on the basis of critical temperature of super heavy oil) of heated area and production time under different soaking time is established. This relationship is related to radial distance and time during oil flowing from effective temperature field boundary into wellbore so that maximum drainage radius and corresponding production time of oil well under different soaking time are obtained. Therefore optimum soaking time is determined with fluid production being maximal as objective function. Good results have been achieved in field application of this method.