Projects managers normally seek to lower the extent of risk by signing contracts, such as Design-Bid-Build (DBB) or Design-Build (DB) project delivery systems to transfer or share risk over to other project entities. The main purpose of this study is doing risk assessment from the perspective of clients, comparing project delivery systems mentioned above to see, firstly, what risk factors are, and, secondly, to analyze the ranking of risk factors and amount of risk with temporal sequencing change over different project stages (e.g. proposal surveying, scheme designing, procurement contracting, and construction receiving). Thus, identify risk factors using literature reviews and conduct survey with clients; utilize the fuzzy numbers with integral value to simulate the changes of ranking of risk factors and the amount of risk with temporal sequencing, given different the attitude of decision makers in risk management (pessimistic, neutral, or optimistic) of the decision-makers towards risk, meanwhile, consider information accuracy in decision-making environment. The result shows that Design-Bid-Build mainly concern about quotation, cost, drawing specification, etc. Furthermore, many risks arise in earlier stage, such as proposal surveying stage and scheme designing stage, that the practice of Design-Build should exert precaution to prevent likelihood of contractors using inferior materials to cheat profit out of affirmed bidding assignment, drawings, etc., and that risks are higher in proposal surveying stage and procurement contracting stage.