The invention discloses an internal matching design method of increasing large power LDMOS device stability. A polycrystalline resistor R is added on a pipe core layout of a ''T''-type network structure formed by a traditional LC. In the invention, through adding the polycrystalline resistor R on the existing pipe core layout, negative feedback is formed in a chip and a gain is reduced so that a device can be maintained in a stable gain range, integral work stability is increased and purposes of improving a matching structure and increasing stability are further reached. The method can be used for internal matching packaging of a radio frequency microwave large power device.