The invention discloses a double-frequency power divider based on a slot line and a design method of the double-frequency power divider, and relates to the field of microwave techniques. The slot line replaces an isolation resistor, and therefore it is avoided that lumped elements need to be arranged between output ports to achieve the isolation function of an existing double-frequency power divider; high isolation between the output ports at two working frequency bands is achieved through double-frequency resonance of the slot line, power distribution at a given frequency and matching of all ports can be achieved, good isolation between the output ports at double frequencies can be achieved as well, and therefore the defect that lumped elements are needed for achieving the isolation function of an existing Wilkinson power divider is overcome. The double-frequency power divider based on the slot line and the design method of the double-frequency power divider are especially suitable for power divider circuits with lumped elements needing to be arranged on interlayers of multilayer circuit structures such as LTCC and MICs and beneficial for integrated design and implementation of circuits, and can guarantee the reliability and stability of the circuits. The double-frequency power divider based on the slot line and the design method of the double-frequency power divider can be applied to feed networks and microwave power distribution/synthesis networks of microwave antennas and other functional circuit modules of microwave engineering.