On the occasion of the centennial birthday of Mr. Chen-Ning Yang, many articles have summarized his important scientific influences on the development of contemporary physics. The author thinks that, as one of the greatest theoretical physicists, Mr. Yang in many scientific contributions has promoted the revolutionary progress of physics, and his unique style of science with deep and meaningful thoughts in academia has a long-term inspiration on developments of physics. Learning from Chen-Ning Yang's scientific thoughts, the author will put forward some personal opinions on the development trend of theoretical physics with his own experiences in researching theoretical physics for 30 years, e.g., studies of quantum open system, superconducting phase transition and cold atom physics by following Mr. Yang in Stony Brook from 1992 to 1994. This article will elaborate why it is important to pursue “beautiful or useful” theoretical physics through some concrete illustrations; Why could the good theories in fundamental physics be kept at a distance from experiments for some time? For the latter, this article also argues the relationship between theoretical prediction and experimental confirmation from the perspective of scientific methodology (philosophy). Focusing on “useful” theoretical physics-the applied theoretical physics, the author emphasizes that scientific research driven by the national demand, as well as free exploration, can also lead to important breakthroughs in fundamental physics.