The present disclosure provides a flexible circuit board, a light bar, a light source and a display device. The light source includes a flexible circuit board having at least one effective welding portion and a light bar having at least one effective pad, the at least one effective welding portion being in one-to-one correspondence with the at least one effective pad, and the effective welding portion being fixed to a corresponding effective pad to transmit a signal loaded by itself to the corresponding effective pad. The flexible circuit board further includes at least one auxiliary welding portion, the light bar further includes at least one auxiliary pad that is in one-to-one correspondence with the at least one auxiliary welding portion, and the auxiliary welding portion is fixed to a corresponding auxiliary pad to enhance the firm fixing between the flexible circuit board and the light bar.