"非教会派的新教徒" can be translated as "non-conformist Protestants" or "dissenting Protestants".
Both expressions are commonly used in English to refer to Protestants who do not adhere to the established or state-supported churches (such as the Church of England in the UK). "Non-conformist" emphasizes their refusal to conform to the practices or beliefs of the mainstream church, while "dissenting" highlights their opposition or disagreement with the established church.