Critical flow Venturi nozzle (CFVN) is a standardized gas flow distribution device widely adopted in the petrochemical industry due to its simple structure and excellent stability. This article summarizes the critical applications of CFVN in the distribution of feedstock across the radiation section tubes of ethylene cracking furnaces, and elaborates on its importance in ensuring the uniform distribution of cracking feedstock, maintaining the stable operation of cracking furnace, and extending the operating cycle. The working principle of CFVN based on critical flow condition (where flow velocity reaches sonic speed) is introduced in detail, emphasizing that a back pressure ratio (outlet pressure / inlet pressure) below the critical value is the key condition for achieving uniform distribution. Utilizing a combination of industrial case studies with specialized software and Computational Fluid Dynamics (CFD) simulations, this article investigates the flow characteristics of compressible turbulent within the CFVN. The analysis focuses on the significant impact of throat diameter and diffuser length on the back pressure ratio and pressure drop. CFD results show good agreement with industrial operational data, validating the simulation approach. Key findings indicate that increasing the throat diameter elevates the back pressure ratio, potentially nearing its critical limit, while an optimal diffuser length minimizes pressure loss effectively. These insights provide essential theoretical foundations and practical references for the optimized design of CFVNs in ethylene cracking furnaces, balancing distribution uniformity with energy efficiency.