Black phosphorus (BP) presents high theoretical capacity as potassium-ion battery (PIB) anode, while low ionic/electronic conductivity for bulk phase and high volume expansion and extremely sensitivity to humid environment for its nanomaterial hinder its practical applications. Here, we propose BP nanocomposites with amorphous zinc phosphate to tackle above problems. The amorphous zinc phosphate plays multifunctional roles in weakening the agglomeration of BP nanomaterials, reducing the volume expansion and improving the environmental stability of BP nanocomposite electrodes in humid air. The optimized amorphous BP nanocomposite anode with 30wt% zinc phosphate, BP@C@ZPO(30), retains capacity of 369.0 mA h g^–1 after 500 cycles at 0.5 A g^–1 in a noninflammable triethyl phosphate (TEP) electrolyte, and the volume expansion rate of the BP@C@ZPO(30) electrode is reduced to 47% compared with BP@C@ZPO(0) electrode of 100%. More attractively, the amorphous zinc phosphate improves the environmental stability of the nanocomposite electrode in humid air dut to its features of strong and fast physical absorption to water. Consequently, the BP@C@ZPO(30) electrode delivers a reversible capacity of 629.2 mA h g^–1 (200 cycles at 0.2 A g^–1) even after exposing the electrode to humid air for two days. Such nanocompositing strategy may accelerate the practical application of phosphorus electrode.