The invention discloses a clamp-type measuring device for small alternating-direct current. The device comprises a sensing head, a modulation transformer, a band pass filter, a phase-sensitive demodulator, a direct-current amplifier, a power amplifier, an alternating-current filter amplifier, a coupling capacitor and a standard resistor, the sensing head comprises upper and lower semicircular U-shaped detection iron cores, the upper semicircular U-shaped detection iron core comprises first and second semicircular detection iron cores, the lower semicircular U-shaped detection iron core comprises third and fourth semicircular detection iron cores, and the first, second, third and fourth semicircular detection iron cores are wound with first, second, third and fourth modulation detection windings respectively; the outer faces of the upper and lower semicircular U-shaped detection iron cores are wound with fifth and sixth alternating-current detection windings respectively. The upper andlower semicircular U-shaped detection iron cores after being assembled are integrally put into a half cavity of an annular magnetic shielding iron core composed of two semicircular magnetic shieldingiron cores, and a feedback winding is wound outside the annular shielding iron core. The modulation detection windings and the alternating-current detection windings respectively measure direct-current and alternating-current components of measured current so as to realize measuring of small alternating-direct current.