A signal separation method, a pixel unit, and a pixel array are provided. The method comprises: determining a first threshold voltage between a first primary node of at least two primary nodes that stores first radiation charges and an adjacent subsequent-stage and controlling, when a second primary node of the at least two primary nodes that stores second radiation charges is electrically connected with an adjacent subsequent-stage node, a second threshold voltage between the second primary node and the adjacent subsequent-stage node so that echo radiation charges in the second radiation charges are transferred to the subsequent-stage The second threshold voltage is equal to the first threshold voltage; the first threshold voltage is used to make the background radiation charges included in the first radiation charges fully or partially remain in the first primary node when the first primary node is electrically connected with the subsequent-stage node.