We assessed the pivotal effect of YAP on the proliferation of human bladder smooth muscle cells (hBdSMCs) under different ECM stiffnesses. We investigated the interaction between YAP and Smad3 through mass spectrometry and immunoprecipitation (IP). Transcriptome sequencing was used to predict the phenotype and signalling pathways. CUT and TAG sequencing was utilized to analyse the target genes of Smad3, and a dual-luciferase reporter assay was used to confirm the sequencing results. The YAP inhibitor CA3 was used in a partial bladder outlet obstruction (pBOO) rat model construction to evaluate bladder smooth muscle proliferation in vivo.