The invention discloses a method and a system for dynamically monitoring the software service quality based on Bayesian inference. The method comprises the following steps of: setting null hypothesis and alternative hypothesis, selecting a prior distribution function, reading a training sample, pre-processing the training sample, counting the quantity of samples meeting attributes, and updating a sample set; reshaping the total quantity of samples, the quantity of successful samples and a standard value; and calculating a Bayesian factor, and analyzing, storing and returning a monitoring result. The system comprises a controller, an observer and an analyzer, wherein the controller is used for acquiring the service statement of software, generating an analyzer of different task objectives, transmitting a service standard required to be matched to the analyzer, issuing a command to a data acquisition end, and controlling periodic acquisition; the observer is used for periodically acquiring needed service data from a data service end, and screening, classifying and rearranging information; and the analyzer is used for matching data to form a sample which can be pre-processed, transmitting into a history database for storing, analyzing data by adopting a Bayes statistical module, and storing a result into a monitoring result database.