Abstract: A method for estimating capacitance applied to a three phase converting device is disclosed. The three phase converting device includes a three phase converter and a processor. The processor executes following steps: (a) outputting a non-baseband signal to the three phase converter, such that a bus voltage of the three phase converter generates a non-baseband flutter; (b) obtaining the bus voltage of the three phase converter; (c) obtaining a bus voltage estimating value based on the bus voltage, a bus capacitance estimating value, an input power, and an output power of the three phase converter; (d) respectively outputting a first AC component and a second AC component corresponding to the non-baseband flutter through filtering the bus voltage and the bus voltage estimating value by a filter segment; (e) estimating a bus capacitance based on the first AC component, the second AC component and a bus capacitance initial value.