Anti-slipping safety factor between the main cable and saddle, deflection-to-span ratio of main girder and force in the mid-tower, which are not important factors in two-tower suspension bridge design, yet becoming dominant ones in three-tower. Moreover, these factors are all controlled by live load. Thus geometrical nonlinearity under live load for three-tower suspension bridge becomes even more significant. This paper takes Taizhou Yangtze River Bridge as the study object, and uses linear deflection theory, incremental UL formulation and total CR formulation to study the geometrical nonlinearity of various key responses of the structure under live load. It is concluded that accuracy and efficiency of total CR formulation is the highest among the three as well as the maximum error of incremental UL formulation is no more than 0.3%; however, the error of widely used linear deflection theory is 6.6%, 4.5% and -2.64% respectively, which is conservative and can not meet the requirements of sophisticated analysis.