Errors of two Inverse Perspective Mapping (IPM) formulae are analyzed in mathematics,and a new IPM formula is deduced.An experiment is designed to validate the IPM result from different formulae.Experimental results show that,whatever the parameter of camera is,the IPM result obtained by the third formula has no distortion.In the special condition of camera installation,the average error of the deduced formula is 0.85%.Consequently,the IPM transform result of the improved formula is more precise and can satisfy the system requirement in smart navigation and road surface reconnaissance field.