This paper is concerned with characteristics of air duct of small-scale refrigeration installation with air forced convection cooling. The subject of this thesis is a domestic indirect cooling electrical freezer-refrigerator. A model and corresponding computer code of three-dimensional air flow in it are developed with Finite Volume Method and SIMPLEST algorithm in original variable form at general curvilinear coordinate. Distribution characteristics of the flow field and pressure loss are analyzed. Experiments are performed and have confirmed the numerical results. A model of the fan for performance prediction is proposed. At the same time, the authors have carried out the experiment of the factual product, the result of test has shown the validation of the model. As we know, the fan is always operating with the air duct. So analyses are made on the coupled relationship between the fan and the air duct. On the basis of them, the authors have been studied the changing parameters of the operating point. The optimal design of the air duct is also discussed. At last, the authors propose a practicable method of electing and designing the fan.