Abstract: In order to establish a method,which is consistent with the current bridge design Specifications,for load rating the existing bridges,load capacity checking factors are calibrated based on reliability theory.Firstly,according to the load capacity checking expression of the existing bridges,the assumption that the condition levels of bridges structures or components are equal to reliability-based levels of load capacities is adopted.On the basis of reliability-based rating scales of load capacities,the relations between various condition levels and reduction coefficients of bridges are analyzed.And then the suggested values of load capacity checking factors consistent with the current bridge design specifications are presented.Finally,the correction formula is provided to modify the checking factors by considering the differences of resistance factors between actual values and theoretical values.The research results indicate that the maximum value of load capacity checking factors are 1.0 for various components designed with current specifications which satisfy the target reliability index;The checking factors calibrated by checking formats based on previous specifications are consistent with these adopted in current specification for load capacity rating of highway bridges.