Abstract: A method for counting a number of people based on appliance usages and a monitoring system using the same method. The method includes the following steps: collecting first numbers of people and first appliance usages corresponding to a first time duration in a specific space; establishing a predictive model related to the first time duration according to the first numbers of people and the appliance usages; detecting a second appliance usages in a second time duration; predicting a second number of people corresponding to the second time duration and the second appliance usages according to the predictive model.