The invention discloses an evaluation method for a static load performance of a railway steel bridge based on a static strain extremum prediction, which relates to an evaluation field of the static load performance of the railway steel bridge. The evaluation method for the static load performance of the railway steel bridge based on the static strain extremum prediction includes the following steps. 1) Strain data of the least favored area of key components of the railway steel bridge is collected. 2) Static strain constituents of the strain data is extracted by utilizing a wavelet packet analysis method. 3) A diurnal variation extremum of the static strain constituents is obtained by using a first-order difference. 4) A cumulative distribution character of the diurnal variation extremum is fitted through using a generalized extremum value distribution function. 5) The static load performance of the least favored stress area of the key components of the railway steel bridge is evaluated. The evaluation method for the static load performance of the railway steel bridge based on the static strain extremum prediction can effectively avoid that a strain maximum or a strain minimum is not the strain extremum, and make extracted strain extremum data more accurate, and guarantee uniqueness of probabilistic statistical characteristics of the strain extremum.