This instrument is used to determine the migration coefficient of the unsteady migration of chloride ions in concrete (NT Build492, national standard and highway standard) to determine the resistance of concrete to chloride ion penetration and reflect the concrete's impermeability (compactness). The instrument consists of a diffusion coefficient tester host, a diffusion coefficient test fixture and a fully automatic vacuum water retention machine. The key components such as the power supply are imported with original packaging. The independently designed software and hardware have good compatibility, real-time data display, automatic storage, and automatic recovery after interruption; High precision, low energy consumption, durable and other characteristics; the overall structure is simple and generous, stable operation, safe and reliable.