The invention relates to a combined treatment method for heavy metal sludge and waste acid, and belongs to the technical field of heavy metal sludge resource comprehensive utilization. The combined treatment method comprises the following steps: first, naturally drying the heavy metal sludge; then, crushing the naturally dried heavy metal sludge to the particle size of 1 to 10 mm; next, adding the crushed heavy metal sludge into the waste acid, stirring for 5 to 15 hours at normal temperature to make the mixture emulsible, and performing solid-liquid separation to obtain leaching liquid and arsenic removal sludge; later on, concentrating the leaching liquid at a low temperature, cooling and crystallizing the concentrated leaching liquid to obtain primary concentrate and crystallized coarse As2O3; finally, washing the obtained arsenic removal sludge with clean water to obtain a washing solution and washed sludge, solidifying the washed sludge by a conventional method to obtain a solidified product, washing the washing solution and the obtained primary concentrate with acidic gas, and returning the washed washing solution and the primary concentrate as the waste acid. According to the method, wastewater is not generated and secondary pollution is not caused in the treatment process; the finally obtained arsenic trioxide also has an economic value.