The Carbon Intensity Indicator (CII) plays a critical role in assessing vessel efficiency. This study examines the impact of cold ironing (CI) on CII performance by analyzing 183 voyages of container ships. The research evaluates the attained CII values, CII ratings, and a Levelized Cost of Energy (LCOE) under different voyage data of container ships between 2023 and 2030. Results show that while 90.7% of voyages met the CII reference value in 2023, this rate decreased to 68.9% and 19.7% by 2026 and 2030, underscoring the increasing challenge of regulatory compliance, if no energy efficiency measures can be taken. Seasonal variations significantly influenced the CII, especially in March and May. With the implementation of CI on container ships, 6441.95 tons of heavy fuel oil and 6101.77 tons of marine gas oil consumption have been eliminated during port stays based on voyage data. Economic analysis indicates that CI increases the LCOE by 13.76%-19.65%, with a discounted payback period ranging from 4.69 to 24 years. This study highlights CI as a viable short-term measure for reducing maritime emissions and enhancing CII compliance, emphasizing the need for optimized economic models.