Adenosine-to-inosine (A-to-I) RNA editing is a critical post-transcriptional modification that diversifies the transcriptome and influences various cellular processes, yet its regulatory mechanisms remain largely unknown. Here, we present two complementary CRISPR-based genetic screening platforms: CREDITS (CRISPR-based RNA editing regulator screening), which enables genome-scale identification of editing regulators using an RNA recorder-based reporter system, and scCREDIT-seq (single-cell CRISPR-based RNA editing sequencing), which provides multiplexed single-cell characterization of transcriptome and editome changes for pooled perturbations. By screening 1,350 RNA-binding proteins, we identified a series of A-to-I editing regulators. Mechanistic investigation revealed DDX39B as a global repressor of A-to-I editing, which functions by preventing double-stranded RNA accumulation through its helicase activity. Targeting DDX39B significantly enhances the efficiency of RNA-editing-based tools, such as CellREADR (cell access through RNA sensing by endogenous ADAR) and LEAPER (leveraging endogenous ADAR for programmable editing of RNA), and disrupts hepatitis D virus (HDV) RNA editing homeostasis. These technological advances not only expand our understanding of RNA editing regulation but also provide powerful tools for exploring tissue-specific and context-dependent RNA modification mechanisms, with broad implications for therapeutic development.