A method for detecting a random missing code by applying a delta-sigma (&Dgr;&Sgr;) analog digital converter having a digital filter is provided. The method includes steps of floating an input end of the delta-sigma (&Dgr;&Sgr;) analog digital converter, and detecting an output code outputted from the digital filter of the delta-sigma (&Dgr;&Sgr;) analog digital converter for determining whether the random missing code exists. A detecting device for detecting the random missing code is also provided.