Equivalence is one of the key aims of Translation Theory. The amount of the semantic and stylistic information that is going to reach the recipient depends on the level of equivalence. With an increase of translatable cinematography, the significance of equivalent translation rises, since it is able to transmit the core script ideas to the audience. Foreign animation translation attracts interest due to the cultural information exchange between different ethnic groups in an unobtrusive and entertaining way. The scientific novelty of this research consists in a specific way of analysing the idiom corpus, since we have examined not only the original translation of the “Hey, Arnold!” TV-series and the idioms' denotations, but also we have used etymological dictionaries in order to fully show the connotation of set-expressions and to find equivalents and analogues in the translating language based on similarities of origin. The purpose was to discover the most efficient ways of achieving equivalence in idioms translation from English into Russian. To accomplish this goal, the following tasks were set: to examine the ways of idioms translation, to learn about equivalence concepts, to find idiomatic expressions in the “Hey, Arnold!” TV-series, and to analyse the equivalence of the original and translated utterances. The outlined tasks required the following set of methods: comparative, contextual analysis, quantitative calculation. Upon analysing 100 units from the TV series, we came to conclusion that the translators mostly used the semantic translation rather than the nominal one. Concerning levels of equivalence, the majority (thirty three units) achieved the level of message, equal number (twenty five in both cases) reached the levels of utterance and situation description, followed by eleven of communication purpose, and six of language signs levels. We have concluded that such distribution appeared because the Russian language does not have enough equivalents that would coincide with those of the English language in syntax, national colouring, created image. The reason for that is the difference of extralinguistic factors influencing the nation's vocabulary and idiomatic layer. Message level is enough to transmit the most part of the underlying information, however, some stylistic colouring shades may get lost in the translation process.