The invention discloses a plastic connecting piece, and a connecting structure of a PCB and a fixed board, and relates to the field of electronic assembling. The plastic connecting piece comprises a connecting piece main body, a first clamping arm, a second clamping arm, a positioning column and a pre-positioning part, wherein the first clamping arm and the second clamping arm are arranged on the front surface of the connecting piece main body and are arranged oppositely; the first clamping arm comprises a fixed section connected with the connecting piece main body and an elastic arm; a first clamping hook block is arranged on the side surface of the elastic arm; the second clamping arm is provided with a second clamping hook block; the positioning column is arranged on the back surface of the connecting piece main body; the pre-positioning part comprises a connecting part which protrudes from the back surface of the connecting piece main body and a clamping part arranged on the end part of the back surface of the connecting part; and a gap is formed between the clamping part and the back surface of the connecting piece main body. According to the plastic connecting piece and the connecting structure, the PCB can be clamped and fixed through the first clamping arm and the second clamping arm; then the connecting piece main body is fixed on the fixed board through the pre-positioning part and the positioning column; and therefore, the PCB can be tightly fastened on the fixed board without requiring screws quite conveniently.