The invention provides an identification method of the on-off state of an air conditioner. The identification method comprises the following steps that S11, sample data are collected; S12, the sample data are preprocessed, and abnormal samples are filtered out, so that preprocessed samples are obtained and divided to a training set and a testing set; S13, characteristic item selection is conducted on the training set to obtain characteristic items; S14, the characteristic items are processed to obtain identification rules of the on-off state of the air conditioner, wherein the rules comprise temperature and humidity sections and the corresponding on-off state of the air conditioner; S15, the testing set is used for testing the identification rules to obtain a test result; S16, whether the test result is larger than a preset threshold is judged, if yes, the identification rules are used as an identification result, and if not, the S13-S16 steps are executed repeatedly until sample data testing is completed. The method is high in accuracy, good in real-time performance, efficient and convenient to implement. The invention further provides an identification system of the on-off state of the air conditioner and an estimation method and system of the on-off state of the air conditioner.