The loads and load combination in ballastless track design was briefly introduced. The influence of cracks to the track slab flexural stiffness was studied. According to the mechanical characteristic of ballastless track, the structural coefficient was proposed and put to use in the amendment of different load effect on track slab. The prerequisite of the combination of moment and tensile force was discussed. Take the track slab in bi-block ballastless track for example, the reinforcement in segmental slab and continuous slab was calculated respectively. The results show the reinforcement ratio will substantially reduce when the structural coefficient was considered in the design. In general circumstance, the thermal force in continuous track slab will cause relatively large cracks, in which condition the bending effects cannot be added. The reinforcement in segmental track slab was controlled by train loads, while that in continuous track slab was controlled by thermal force.