Harmanli municipality is in the centre of Haskovo region. Its territory spreads over some parts of the Upper Thracian lowlands between the oblique south slopes of the Sredna Gora and precipitous north slopes of the Rhodope Mountains. The south boundary of the Thracian lowlands is outlined by the north Rhodope foot, along which it leans close on the north Rhodopes, between the lower end of the Momina Klisura defile (at 300 m elevation) and the beginning of the Harmanli defile (at 80 m elevation). The current of the Maritsa River flows near along the whole extent of this boundary, dividing the municipality into two almost equal parts. The tributaries of the Maritsa River, Harmanli and Bisser rivers flow through it as well.