The magneto-optical spectra of ABC-stacked trilayer graphene are enriched by an electric field. A lot of prominent absorption peaks, which arise from the inter-Landau-level transitions, gradually change from twin-peak structures into double-peak ones with increasing electric-field strength. This comes from the destruction in mirror symmetry of the xy-plane and the non-equivalence of two sublattices with identical projections. Specially, a single threshold peak becomes a double-peak structure, owing to the Fermi–Dirac distribution. The absorption frequencies continuously grow or decline except for those caused by the anti-crossings of Landau levels. Also, such anti-crossings can induce extra double-peak structures.