To provide a system and a method for plant data distribution which enable adequate repair by monitoring and diagnosing plant data at low cost while improving the frequency and precision.

The plant data distribution system 10 is constituted by connecting a data distributing server 17, a data gathering and processing device 21, and a monitoring and diagnosing device 23 by communication networks 14, 14a, and 14b, and stores plant state quantity data from the data gathering and processing device 21 on the data distributing server 17, adequately transmits the stored plant state quantity data to the monitoring and diagnosing device 23 to monitor and diagnose plant equipment 19, and stores monitoring/diagnostic results on the data distributing server and then distributes them to the data gathering and processing device 21.