This　paper　presents　an　improved　ultrashort　wave　single-channel　Doppler　direction　finding　system.　The　circuit　method　of　comparator　+　mid-band　pass　filter　is　proposed　and　analyzed　to　eliminate　the　influence　of　incoming　wave　amplitude　modulation　information　on　direction　finding.　An　electronic　switch　switching　frequency　adaptive　algorithm　is　proposed　to　eliminate　the　influence　of　the　arrival　frequency　(phase)　modulation　information　on　the　direction　finding,　that　is,　the　method　of　using　software　to　control　the　electronic　switch　switching　frequency,　programmable　bandpass　filter　center　frequency　and　bandwidth.　When　the　switching　frequency　of　the　electronic　switch　is　zero,　the　software　calculates　the　appropriate　switching　frequency　of　the　electronic　switch　and　the　narrowband　bandwidth　of　the　programmable　bandpass　filter　based　on　the　analysis　of　the　arrival　wave　spectrum　characteristics　to　give　the　horizontal　angle　of　the　arrival　direction.　This　article　gives　an　algorithm　for　the　horizontal　angle　of　the　arrival　direction.