Abstract: An online measurement method for temperature stability of production layers in an oil and gas well includes: obtaining a plurality of temperature data at each position point of an optical fiber; according to the temperature data, calculating temperature standard deviations of each position point within a production layer at a plurality of time points; performing probability distribution statistics according to the temperature standard deviations at all position points of the production layer at a same time point, fitting a probability distribution curve according to normal distribution, and obtaining a probability density function; obtaining the temperature standard deviations corresponding to at least one value that integral values of the probability density function at all position points of the production layer at each time point is between (0, 1), generating a standard temperature deviation normal distribution probability time curve of each section of the production layer according to the temperature stan