Abstract: The lateral horizontal load acting on segments might be divided into three parts as the water level was located within tunnel section: rectangular load,full-span(span height equal to tunnel diameter) triangular load and non-full-span triangular load.The existing modified methods might only deal with the third one approximately,and resulted in calculated results with errors.The non-full-span triangular load was dealt with as follows: firstly,deducing the elastic solution of internal force of the segments under the action of the load;secondly,converting the load intensity to the equivalent full-span one according to the laws of equivalent area.The equivalent intensity was used to calculate horizontal soil reaction and internal force of segment.With regard to four typical shield tunnels in China,the influence of water level variation on internal force of segment under different overburden thicknesses was studied using the deduced formula and the existing modified methods.The variation laws internal force of segment were obtained.It might be helpful to the structural design.