This　paper　studied　the　stability　and　Hopf　bifurcation　of　a　type　of　protein　synthesis　system　with　time　delay　and　negative　feedback.　Firstly,　it　is　proved　theoretically　that　the　time　delay,　nonlinearity　in　the　protein　production　and　the　cooperativity　in　the　negative　feedback　are　key　factors　to　generate　circadian　oscillation;　Taking　time　delay　as　a　parameter,　we　obtained　the　critical　value　of　the　time　delay　that　Hopf　bifurcation　generates.　Secondly,　based　on　the　center　manifold　and　normal　form　theorem,　we　derived　the　formulas　for　determining　the　stability　of　bifurcating　periodic　solutions　and　the　supercritical　or　subcritical　Hopf　bifurcation.　Finally,　the　matlab　program　is　used　to　simulate　the　results.