The invention discloses a seat cushion adjusting mechanism of an integrated automobile safety seat for children, which comprises a seat cushion height adjusting mechanism and a seat cushion length adjusting mechanism, wherein the seat cushion height adjusting mechanism is installed below the middle seat cushion of the back-row seats, and the middle seat cushion of the back-row seats can be liftedby a driving device and a link mechanism, so that the seat for adults can be changed into a heightened seat for children; and the seat cushion length adjusting mechanism is connected with multiple sections of additional seat cushions which can be connected with or separated from each other at the front side of the seat cushion of the seat, so that the length of the seat cushion can be adjusted according to the body sizes of the children. The invention can realize the stepless adjustment of the seat cushion height based on the height of the children and the multistep adjustment of the seat cushion length, thereby protecting the children from being hurt in the process of automobile collision when being used by matching with the traditional three-point safety belt for adults. Besides, the invention can be adjusted to adapt to adults for use, has the advantages of simple structure, low cost and convenient use, and can realize the intelligent positioning of the children.