The invention relates to the field of engineering construction, in particular to an in-service bridge pile foundation side friction calculating method considering a load bearing process influence. The method comprises following steps: A, according to the stratum depth, a pile foundation is divided into N segments, the stratum corresponding to the pile segment i is marked as the stratum i; B, according to differences of pile foundation load bearing, a pile forming stage, an operating stage and a transforming stage are included, and the total stress P0i, P1i and P2i of surrounding soil of piles of the layers i of the three stages is calculated; C, the stratum i is subject to sampling, the soil initial void ratio e0i is measured, the compression test is carried out, and the surrounding soil initial void ratios e1i and e2i of stratum piles i corresponding to the P1i and P2i are obtained; D, side soil compression modulus Es1i and side soil compression modulus Es2i of the stratum piles i of the operating stage and the transforming stage are calculated; E, according to the side friction initial standard value tau0i of the stratum i of the pile forming stage, the side friction initial exerting value tau1i of the stratum i of the operating stage, the compression modulus Es1i and the compression modulus Es2i, the side friction standard value tau2i of the stratum i of the transforming stage is obtained through calculation. Through processing of the above steps, precision of the finally-calculated side friction standard value can be ensured.