The present invention discloses a digital-to-analog conversion apparatus having current source measuring mechanism. A digital-to-analog conversion circuit in turn sets one of thermo-controlled current sources as an initial current source to operate according to two specific input codewords included in an input digital signal to generate an output analog signal. The values of the output analog signal corresponding to the two specific input codewords have opposite signs and the same absolute value. An echo transmission circuit processes the output analog signal to generate an echo signal. An echo-canceling circuit processes the input digital signal according to echo-canceling coefficients to generate an echo-canceling signal and receives an error signal to converge the echo-canceling coefficients. A current calculating circuit generates converged coefficients statistics values and perform calculation thereon with a predetermined inverse matrix to generate a current amount of each of the thermo-controlled current sources. An error calculation circuit subtracts the echo signal and the echo-canceling signal to generate the error signal.