The invention discloses a data collection method, device and system. The method comprises the steps of detecting whether uncollected log data written by a writing-in thread meets a splitting condition or not is detected; if the condition is met, the log data meeting the splitting condition is split, saved as a novel log file and stored under a designated directory; the collection thread collects the novel log file under the designated directory and sends the novel log file to a server. It is thus clear that the log data meeting the splitting condition is split and saved as the log file, in this way, the writing-in thread can continue to write in log data when the collection thread works, so that transmission delay is shortened, the working efficiency is improved, and the problems that the collection waiting time is long, and the coherence and efficiency of the overall process are poor due to the fact that the writing-in process and the collecting process cannot be performed at the same time in the prior art are solved.