Several analog signal transmission system under harsh electromagnetic interference environment was introduced, and a method of transmission was designed. Firstly, the analog signal was converted into a frequency signal through the detector and sent through the fiber transmitter. Secondly, the fiber signal was received and the frequency of the optical signal was measured within the configurable regularized time and then the analog signal was calculated instead of using the traditional method which converted analog signal to digital signal after frequency-to-voltage conversion. This system not only got the reduced total conversion time and improved response speed, but also can obtain different precision according to system requirements by adjusting converting time. Tested on a 248 nm KrF excimer laser, the system realized high-precision online monitoring of the slow-changing working gas pressure signal compared with traditional method, and then it also measured the fast-responsed energy signal of pulse laser up to 90 Hz well. By calculating the Pearson coefficient, the acquired value of the scheme tends to be consistent with the original signal to meet the application requirements.