The invention discloses a junction box for a solar cell. The junction box includes a box body, wherein the box body is provided with a plurality of conducting pieces for connecting solar cell pieces; two adjacent conducting pieces are connected by a diode; the conducting pieces at both ends are connected to the outside via a guide line respectively; and the chip area of the diode in the middle is bigger than that of the diodes at both sides. According to the invention, the diode with bigger chip area is employed in parts where the temperature rise is easily produced to reduce the temperature rise; while the diode with smaller chip area is employed in parts where the temperature rise is not easily produced to control cost.