This paper presents an approach to predict the far field sound pressure for a diesel engine using the inverse boundary element method. In this approach, near field sound pressure is measured first. The particle velocity is then reconstructed to a virtual plane instead of the actual vibrating surfaces and the far field sound pressure can be predicted using the reconstructed particle velocity of the virtual plane. Two sets of inverse sound pressure are employed to validate the approach. One is from the finite element and boundary element methods. The other is from the sound pressure measurement of a diesel engine in a hemi-anechoic chamber. Good correlations between the predicted and the measured sound pressure demonstrate that the method can be used to accurately predict the far field sound pressure.