Abstract: The present invention provides a crane boom with multi main chord consisting of an underpart boom sections, an insert jib section and a boom head connected in turn. Said underpart boom sections and insert jib section are multi-main-chord boom sections, there is a main-chord on each of the angle part of the cross-section of the multi-main-chord boom section. Said main-chords are connected one another by several belly bars. Add at least one main-chord on the angle part of the cross section along the width or the height of said multi-main-chord boom, and the added main-chord parallels to the original main-chord. The crane boom with multi main chord of the present invention, without changing the size of the boom sections during transporting, the cross-sectional area of the main-chord is increased and the integral stiffness of the boom is strengthened by increasing main-chord number of boom, thus fold increasing the structural carrying capacity of the boom which is suitable for large crane.