The theory on optical coherence modulation using 2-D ultrasonic standing waves is reported and corresponding analyses are made. Theoretical results show that when 2-D ultrasonic standing waves are used, the phase difference between two ultrasonic waves (i. e., correlation coefficient) with the same frequency and correlated phase has strong influence on modulation of coherence degree and that effect is small when ultrasonic travelling wave are nsed.Also reported are the preliminary measured results on coherence degree modulated with 2 D ultrasonic standing waves excited by two cross electrodes and AO-EO resonant coupling effects of LN EO-crystal respectively. The results agree with the theoretical analysis.