This　work　proposes　a　covert　communication　scheme　in　a　cognitive　radio　network　where　a　secondary　transmitter　(ST)　transmits　confidential　information　to　a　secondary　receiver　under　the　cover　of　jammers　with　homogeneous　Poisson　point　process.　Specifically,　we　first　analyze　the　detection　performance　of　the　primary　transmitter　(PT)　and　Willie　under　collaboration　and　non-collaboration　modes.　We　then　derive　the　covert　transmission　outage　probability　under　ST＇s　correct　and　incorrect　decisions　for　whether　PT　transmits　or　not　and　obtain　the　expression　for　the　effective　covert　rate　(ECR).　In　order　to　maximize　the　ECR,　we　derive　the　optimal　value　of　the　time　allocation　ratio,　based　on　which,　we　also　derive　the　optimal　value　of　ST＇s　transmit　power　subject　to　the　covertness　constraint　and　some　power　constraints.　Our　examination　shows　the　non-collaboration　mode　outperforms　the　collaboration　mode　in　terms　of　achieving　a　higher　ECR,　because　the　uncertainty　of　the　PT＇s　transmission　in　the　former　one　will　cause　confusion　at　Willie　and　lead　to　an　increased　detection　error　rate.　In　addition,　the　proposed　scheme　effectively　increases　the　ECR　when　compared　with　the　scheme　without　the　jammer.