This paper develops a non scanning fiber Fabry Perot demodulator based on correlation demodulation theory. Corresponding theoretical analysis and system optimization are completed. The demodulator uses a liner array CCD as photo detector combining the FPGA and ARM controller to achieve real time signal processing. However, the demodulator can not detect the maximum value of the correlation signal accurately because of the influence of the background noise brought by the unevenness of linear light and the stray light. In order to solve this problem, a signal procession algorithm is proposed. It can filter out the background noise on the correlation signal effectively. Also the detection capability of weak signal and the accuracy of demodulation have been greatly improved, so that the correlation coefficient of the cavity length measurement is 0.999 9 and the fluctuation is only 7 nm. The experimental results indicate that the system can achieve real time measurement, high measurement accuracy, stability and consistency.