A system for diagnosing a pneumatic control valve online, comprising: a sensor set including a plurality of sensors, attached to the pneumatic control valve, for measuring a state of the pneumatic control valve; a smart data analyzer for processing a sensor signal acquired in real time from the sensor set and generating pneumatic control valve state information for online automatic diagnosis of the pneumatic control valve; a data server for transmitting, to an online diagnostic server, the pneumatic control valve state information received in real time from the smart data analyzer and storing the pneumatic control valve state information for a predetermined time period; the online diagnostic server for determining whether the pneumatic control valve is in an abnormal state and generating diagnostic information by comparing the pneumatic control valve state information with pre-stored normal state data of the pneumatic control valve; and a client computer for displaying the diagnostic information received from the online diagnostic server, wherein the data server comprises a raw data transmission manager adapted to transmit the pneumatic control valve state information to the online diagnostic server divisionally while minimizing network bandwidth use amount; and wherein the online diagnostic server is adapted to perform data time synchronization that groups data included in the pneumatic control valve state information based on data collection times, wherein the smart data analyzer is further adapted to generate detail analysis data for user detailed analysis for the pneumatic control valve by processing the sensor signal acquired from the sensor set in real time, wherein the client computer is adapted to receive the detail analysis data via the data server and the online diagnostic server, and to include an analysis tool such that a client is able to analyze a state of the pneumatic control valve based on the detail analysis data, and wherein the data server is adapted to transmit the pneumatic control valve state information to the online diagnostic server with a first time interval, and to transmit the detail analysis data to the online diagnostic server with a second time interval which is longer than the first time interval. a sensor set including a plurality of sensors, attached to the pneumatic control valve, for measuring a state of the pneumatic control valve; a smart data analyzer for processing a sensor signal acquired in real time from the sensor set and generating pneumatic control valve state information for online automatic diagnosis of the pneumatic control valve; a data server for transmitting, to an online diagnostic server, the pneumatic control valve state information received in real time from the smart data analyzer and storing the pneumatic control valve state information for a predetermined time period; the online diagnostic server for determining whether the pneumatic control valve is in an abnormal state and generating diagnostic information by comparing the pneumatic control valve state information with pre-stored normal state data of the pneumatic control valve; and a client computer for displaying the diagnostic information received from the online diagnostic server, wherein the data server comprises a raw data transmission manager adapted to transmit the pneumatic control valve state information to the online diagnostic server divisionally while minimizing network bandwidth use amount; and wherein the online diagnostic server is adapted to perform data time synchronization that groups data included in the pneumatic control valve state information based on data collection times, wherein the smart data analyzer is further adapted to generate detail analysis data for user detailed analysis for the pneumatic control valve by processing the sensor signal acquired from the sensor set in real time, wherein the client computer is adapted to receive the detail analysis data via the data server and the online diagnostic server, and to include an analysis tool such that a client is able to analyze a state of the pneumatic control valve based on the detail analysis data, and wherein the data server is adapted to transmit the pneumatic control valve state information to the online diagnostic server with a first time interval, and to transmit the detail analysis data to the online diagnostic server with a second time interval which is longer than the first time interval.