Background: As increasing evidence showed the efficacy of percutaneous left atrial appendage (LAA) occlusion in reducing the stroke risks in patients with non-valvular atrial fibrillation(AF), we design this study to quantify the effect of surgical LAA occlusion (SLAAO) for patients with valvular diseases and with or without AF. Methods: The current study will be implemented in two parts: Part 1 (AF study) is a prospective longitudinal study with a plan to consecutively register 2032 patients diagnosed with valvular diseases and AF and receiving cardiovascular surgeries. SLAAO will be performed at the individual surgeon’s preference. We centrally conducted a one-year follow-up on stroke, systemic arterial embolism, and all-cause mortality. Part 2 (non AF study) is a single-blinded, multicenter, randomized controlled trial with the purpose to evaluate the efficacy of SLAAO to reduce one-year embolism events in patients with valvular diseases, without AF, and receiving cardiovascular surgeries. 2118 patients will be randomized 1:1 to the intervention or control arm using a central randomization system. Results: The primary outcome is a composition of newly occurred ischemic stroke/transient ischemic attack (TIA) with positive neuroimaging or systemic arterial embolism, and cardiovascular mortality during one-year follow-up. Conclusion: The trial is designed to evaluate the efficacy of SLAAO to reduce embolism events one year after mitral or aortic surgeries, and this paper presents the prospective study protocol. It provides details of patient randomization, follow-up, methods of analysis of the material, and publication plan.