If you are using MultiChain 2.0, use "publishmulti"
For example: publishmulti <stream-name> '[{"key":"A000001","data":"48656C6C6F20576F726C64210A"},{"key":"A000001","data":"00"}]'
or
You can execute an equivalent of multiple publish commands by using createrawsendfrom.
For example:
createrawsendfrom '<address>' , {}, '[{"for" : "stream-name", "key" : "A000001", "data" : "whatever-data"},{"for" : "stream-name", "key" : "A000001", "data" : "other-data"}]', 'send'
PS: This syntax is for linux.
For help with API commands visit: https://www.multichain.com/developers/json-rpc-api/