Abstract: Algorithms concerning phase difference measurement, viz, the zero passage method and the relevant function method are brought forward. The principle involved is introduced, and factors influencing the precision and speed of phase difference measurement are discussed. Judgment of the point of zero passage is the key factor involved, and a higher sampling frequency should be adopted when the method is applied on situations of large signal amplitude. Adopting signal filtration and noise weeding, high precision and fast measurement of phase difference is realized, based on the A/D hardware and a LabVIEW virtual instrument platform. Results of experiment show that the two algorithms put forward in this paper are effective in phase difference measurements of high speed and precision.