The Liberal Democrats plan to scrap business rates to help small firms and will provide greater support for entrepreneurs, if the party wins the general election on Thursday.
Nearly a million businesses in the UK have closed in the past three years, analysis from the Lib Dems suggests.
The party says Brexit uncertainty has added to the high street's demise.
Labour says it will base a network of small business advisers in Post Office branches if it wins the election.
Meanwhile, the Conservatives have said they will reduce business rates for smaller firms and give them a larger discount on National Insurance payments.
Lib Dem leader Jo Swinson is due to visit Hertfordshire on Saturday - Small Business Saturday - to discuss her policies with the owners of small businesses in a bid to convince them to back her party, which is in favour of revoking Article 50 and stopping Brexit.
Citing figures from the Office for National Statistics, the Lib Dems said 978,285 businesses closed their doors between 2016 and 2018 - a 28% rise from the 765,000 that shut over the previous three years.
The Confederation of British Industry (CBI) has previously warned the government of the impact a no-deal Brexit would have on the UK and European Union, saying that leaving with a deal is essential to protect the economy and jobs.
Sam Gyimah, Lib Dem shadow secretary for business, energy and industrial strategy, told BBC Radio 4's Today programme on Saturday that it was "no coincidence" that in a period of such uncertainty, businesses had to close their doors.
Mr Gyimah said: "We have a situation where the Conservatives and the Labour Party are going to throw the economic cards up in the air and gamble with our future. And all the other things pale in comparison when you look at the issue of Brexit and its consequences."
The Lib Dems plan to boost small businesses by replacing business rates with a new land value tax on landlords, and expand the "future high streets fund" to support redevelopment in town centres and high streets.
A new "start-up allowance" supporting business owners with their living costs in their first few weeks is also being pledged.
Chuka Umunna, Lib Dem spokesman and former Labour MP, warned that "crashing out" of the EU would see "even more damage to businesses up and down the country".
Mr Umunna accused the Conservative government of having "completely failed" small businesses, "saddling them with years of Brexit uncertainty and ignoring urgent calls to reform business rates".
"Liberal Democrats are proud to be a party that supports businesses. We will stop Brexit, get back to dealing with the issues that really matter to small businesses, and build a brighter future," Mr Umunna added.