A radar apparatus and a leakage correction method thereof are provided. The radar apparatus includes a transmitter and a receiver. The transmitter includes a sinewave signal generator. The sinewave signal generator generates a sinewave signal. The receiver includes another sinewave signal generator and a correcting circuit. The receiver receives transmitting signals including the sinewave signal from the transmitter. The sinewave signal generator of the receiver generates another sinewave signal according to the amplitude of the transmitting signals or received transmitting signals. The correcting circuit corrects leakage situation on the received transmitting signals according to another sinewave signal. The phasor of sinewave form corresponding to the leakage situation relates to the phasor of another sinewave signal. Accordingly, the performance of receiver may be improved effectively.