Abstract: Simple harmonic wave method is a precise digital computation method for room acoustics.Accuracy is dependent on the number of series terms taken in computation.In this paper we havediscussed the digital coluputation method and series convergence speed and domaim,and shown thedivergence at the sound source position and the difficulty to performing computation at the proximityof the sound source by diagrams.We have also discussed the theoretical errors of sound intensitymeasurement in reverberation sound field.The measurement errors are so great that the measurement isnonsense if one uses an ordinary sotund intensity meter.To average two measurement sound intensitiesat a sound field position by reversing the probe direction can reduce measurement error a great lot.If we can get a precise sound intensity meter with phase diference between two channels within 0.05 degree,the measurement error can be controlled in a reasonable range.