A circuit board assembling system includes a circuit board whereon a slot is formed. The circuit board includes a first region and a second region. The circuit board assembling system further includes a component placement machine, a positioning rod, wherein a first width of the unadjusted positioning rod is larger than a width of the slot so that the unadjusted positioning rod can not pass through the slot, a conveying device for driving the circuit board to a positioning point in a first direction and driving the circuit board to an assembling position in a second direction, and a control unit for controlling the conveying device to drive the circuit board to the assembling position in the second direction and controlling the component placement machine to assemble a first component set and a second component set on the first region and the second region respectively.