In order to improve the accuracy of distributed optical fiber sensing system, the errors standard deviation of temperature and strain in multi parameter simultaneous measurement and single parameter measurement are compared theoretically. It is pointed out that under the typical configuration, the simultaneous measurement error standard deviation of double-fiber or double-wavelength method can reach 9 ~ 850 times that of single parameter measurement method, and the strain error standard deviation of double segment optical fiber method is 1.4 times that of single parameter measurement method. The fitting algorithm based on the pseudo-Voigt model is used to extract the Brillouin frequency shift. The calculation results validate the above conclusions.