Based on the concept of effective working width， the bridge deck is simplified as a multi-span continuous beam. The constraints of the main beam on the bridge deck are equivalent to anti-bending springs. When the stress mechanics of the deck between two main girders is analyzed， this deck is equivalent to a single-span beam. The anti-bending capacities from side spans are also simplified into anti-bending springs. A series of comprehensive equivalent stiffness parameters from the anti-torsion of the main girders and the anti-bending of the side spans are derived recursively. The variations of comprehensive equivalent stiffness parameters against the stiffness ratio of the anti-torsion stiffness from the main girder to the anti-bending transverse stiffness from the bridge deck are studied. The formulae of slopes and moments at endpoint and middle-span point are formulated for the deck constrained by the main girders and side spans under distributing load， concentrated load and partially distributed load， which provides a simplified theory for transverse bending moment calculation of multi-span continuous bridge decks. A background bridge consisting of prestressed-concrete I-type girders and reinforced-concrete bridge decks is studied. The transverse bending moment distributions and transverse bending moment modification factors of different-span bridge decks under model self-weight and automobile section distributing loads are analyzed， and the effect of beam height， deck thickness， beam number and load on transverse bending moment modification factors is investigated. The results demonstrate that： the analytical transverse bending moment from the present theoretical formulae agrees with the finite element， and the equivalent single-span beam method is feasible to simplify the multi-span continuous deck. The maximum result of the transverse bending moment modification factors is 0.666 7 at the supporting point， which is less than the value of 0.7 specified by the Specifications for Design of Highway Reinforced Concrete and Prestressed Concrete Bridges and Culverts （JTG 3362—2018）. When t/h<1/4 （the ratio of the bridge deck thickness t to the main girder height h）， the maximum value of the transverse bending moment modification factors is 0.670 3， which is larger than the value 0.5 specified by JTG 3362—2018. The calculating results based on the specification JTG 3362—2018 are unsafe for the design practice. When t/h>1/4， the maximum value of the transverse bending moment modification factors is 0.679 4， which is less than the value of 0.7 specified by JTG 3362—2018. To ensure the design of the bridge deck safe， further investigation into the transverse bending moment prescribed in JTG 3362—2018 is recommended.