Almost 50 per cent of voters are confused about how the new Senate voting system works and may be unwittingly giving some of their preferences to parties they believe they had put last, a new poll suggests.

The Australia Institute, which conducted the poll, says the Australian Electoral Commission needs to urgently review the instructions it is giving to voters for the May 18 election to ensure people understand what they are doing with their votes.

The Australian Institute poll found almost 50 per cent of respondents were confused about how Senate voting system works. Credit:Janie Barrett

Under the new system for Senate voting, introduced shortly before the 2016 federal election, voters are told to number "at least" six boxes if they are voting "above the line".

Last year, progressive think tank The Australia Institute gave 1450 people the directions from a Senate voting paper and then presented them with a series of statements to test how well they understood the rules.