Robustness　of　digital　watermarking　will　directly　influence　the　application　of　watermarking　technology.　In　order　to　improve　the　robustness　of　CDMA　(Code　Division　Multiple　Access)-based　spread　spectrum　watermarking,　we　propose　two　novel　correlation　properties　of　spread　spectrum　sequence　appropriate　to　digital　image　watermarking:　LAC　(loose　auto-correlation)　and　TCC　(tight　cross-correlation).　Different　from　the　traditional　correlation　properties,　the　new　ones　emphasize　that　whether　sequences　synchronize　or　not　(i.e.,　whether　attacks　exist　or　not),　the　auto-correlation　is　high　and　the　cross-correlation　is　low.　The　comparative　experiment　results　demonstrate　that　the　spread　spectrum　sequences　with　these　new　properties　can　distinctly　improve　the　robustness　of　watermark　algorithms.　©　2014　ISSN　1881-803X.