A method and an apparatus for estimating temperature are provided for estimating a temperature of a test point in a space with an air conditioner. In the method, a first and a second sensor device are deployed in the space, wherein the second sensor device is deployed at the test point. Then, state parameters and temperature transformation functions are defined according to temperatures detected by the first and the second sensor devices and a state of the air conditioner during a predetermined time period. After the second sensor device is removed, a current state of the air conditioner is determined by reference temperatures detected by the first sensor device and the state parameters. One of the temperature transformation functions is selected according to the current state, and a current temperature of the test point is estimated by using the selected temperature transformation function and the reference temperatures.