Abstract: In order to analyze the causes of the abnormal pulse signals sent by the BH-VDT vertical drilling tool when drilling in complicated formations,and to provide the basis for eliminating abnormal pulse signals,by means of laboratory simulation test,the waveforms of normal pulse signals and abnormal pulse signals caused by instantaneous disconnection and underpower were simulated;and the characteristics of such waveforms were analyzed.The results were as follows:the waveforms of abnormal pulse signals caused by instantaneous disconnection showed the characteristics of randomness and diversity,and when the breakpoint appeared in the non-emitted pulse waveband,the amplitude of the waveform was not influenced.The waveforms of abnormal pulse signals caused by underpower showed the characteristics of periodicity and sustainability,and when the breakpoint appeared during the pulse emission,the waveform amplitude was significantly reduced.The causes of abnormal pulse signals could be determined by comparing the characteristics of the waveforms of field acquired abnormal pulse signals with that of the laboratory simulated ones.The applications showed that the causes of abnormal pulse signals could be accurately determined through analyzing the characteristics of the waveforms of field-acquired abnormal pulse signals and comparing them with those of the simulated ones,thus providing a basis for eliminating abnormal pulse signals.