Objective To study the changes of divers' job performance after simulating long-time underwater transport. Methods The long-time underwater transport environment was simulated in the water cabin. The changes of attention, memory, and abilities of emotional regulation, thinking, visual response, tactile response and manual operation were measured at different time points (0.5, 1, 2, 3, 4 and 5 h) with ergonomic tools. Results After stimulating long-time underwater transport, the job performance indexes tested above were all decreased to varying degrees. The overall descent was not obvious within the first 3 h, while it was significantly decreased and showed an accelerated downward trend after simulating long-time underwater transport for 3 h and more, showing significant difference when compared with 0.5 h of simulating long-time underwater transport (all P<0.01). Conclusion Job performance is gradually decreased in divers during simulating long-time underwater transport, and 3-h underwater transport is the limit for current conditions.