Abstract:By applying recursive bandpass filter based on the first-order Butterworth function to running samples,the relative amplitude and phase errors in the output sequence from those running input data are found. The propagation property of the errors in the output is analysed. To suppress the errors of the output,the "three steps recursion technique with developing initial output" procedure has been developed. A lots of tests show that this procedure can suppress the errors and phase shift in the output effectively.