Design and analysis of diaphragm wall requires knowledge on soil mechanics as well as behaviors of strut and wall. The design is generally based upon assumptions that deviate a lot from practice, which may lead to erroneous results. This paper discusses the nature of a few design assumptions, including analysis model, soil strength, modulus of subgrade reaction, water pressure, surcharge loading, preload of struts, etc. The effects of construction control on the behavior of diaphragm wall are also addressed. Basically, the design must rely heavily on experience, or else it may be completely incorrect.