Differentiated somatic cells can be reprogrammed into totipotent embryos through somatic cell nuclear transfer (SCNT).However,most cloned embryos arrest at early stages and the underlying molecular mechanism remains largely unexplored.Here,we first developeda SCNT embryo biopsy system at 2-or 4-cell stage,which allows us to trace the developmental fate of the biopsied embryos precisely.Then through single-cell transcriptome sequencing of SCNT embryos with different developmental fates,we identified that inactivation of Kdm4b,a histone H3 lysine 9 trimethylation (H3K9 me3) demethylase,functions as a barrier for 2-cell arrest of cloned embryos.Moreover,we discovered that inactivation of another histone demethylase Kdm5b accounts for the arrest of cloned embryos at 4-cell stage through single-cell analysis.Co-injection of Kdm4b and Kdm5b can restore transcriptional profiles of SCNT embryos and greatly improve the blastocyst development (over 95%) as well as the production of cloned mice.Our study therefore provides an effective approach to identify key factors responsible for the developmental arrest of somatic cell cloned embryos.