To　overcome　some　drawbacks　of　Viterbi　algorithm　(VA),　such　as　exponential　growing　complexity　of　decoding,　and　its　poor　performance　under　bad　channel　conditions,　some　available　known　information　must　be　used　as　constrained　condition　and　apriori　knowledge　for　decoding.　A　new　constrained　VA　is　proposed　by　adding　constraint　bits　directly　for　conventional　codec.　Compared　with　the　conventional　VA,　under　the　bad　channel　condition,　the　proposed　scheme　can　improve　the　peak　signal　to　noise　ratio　(PSNR)　of　the　decoding　image　2-10　dB　by　changing　the　number　of　constrained　bits.　Experimental　results　show　that　it　is　an　efficient　error-controlling　way　for　the　transmission　of　set　partitioning　in　hierarchical　trees　(SPIHT)　coded　image.