A single-circuit tower with variable nominal height comprises a tower body, a top earth wire cross-arm and pillar insulators. The top earth wire cross-arm is composed of two cross-arms disposed on two sides and perpendicular to a line direction. Each upper cross-over cross-arm is composed of two cross arms on two sides in one tier, perpendicular to a newly-built line direction, and a cross-arm on a single side in one tier. Each middle auxiliary cross-arm is composed of cross-arms on two sides in multiple tiers, perpendicular to the newly-built line direction. A lower pass-through cross-arm is composed of two cross-arms on two sides in one tier, perpendicular to a newly-built line direction. The changes of crossing line reconstruction and cable burying in crossing-before-passing (or passing-before-crossing) engineering are slimmed, outage of crossing lines is avoided, power grid reliability is improved, construction cost is reduced, and the earth wire to ground distance in the passing and crossing grade is further decreased.