Abstract: In the modern fluid mechanics, the flows become more and more complex, that leads to the difficulties in theoretical modelling and analyzing the flow physics. It is known that the theoretical modelling approach, important as experiments and numerical simulations, is part of the applied fluid mechanics, which would be regarded as the application of the engineering science concept proposed by Tsien Hsue-Shen in fluid mechanics. Based on the flow characteristics, the flow can be simplified and the corresponding theoretical model can be established, then it can be solved by mathematical methods and the flow physics can be analyzed. In the present paper, some samples in two research directions were selected to indicate the experience in the practice of applied fluid mechanics.