A circuit sub-board for regulating constant power source and strengthening ground connections. The circuit sub-board is a double-layered printed circuit board having a large surface power-source layer and a ground-connection layer. The circuit sub-board is utilized to cover the insufficiently ground-covered main board signaling lines as well as insufficiently ground-connected power and ground signaling lines on the main board. With the installation of the circuit sub-board, signals can be transmitted more reliably and with less interference.