TOPIC: What does negative total float mean?

Total float = LF-EF=LS-ES
usually finish_time>start_time, how comes negative float?
what does negative float to a project?

Thanks,
Eric

Negative total float effectively means that the schedule cannot be accomplished as planned. Another way of looking at it is that the project will take X (time units) longer than was originally planned.

Example: Total float = -7 days is the same thing as saying the project will take an additional 7 days to finish.