She told MSPs it will hit the people the Tories and LibDems in Westminster claim to be trying to help.
Her comments came as MPs voted on the Government's Bill to limit rises in most working-age benefits to 1% in 2014/15 and 2015/2016 instead of linking them to inflation. They voted 324 to 268, a majority of 56, to give the legislation a second reading.
The aim is to slash £5billion from the welfare bill over the next five years.
But Ms Sturgeon said parents already working hard in low-paid jobs will lose out under the planned reforms.
She said 100,000 would be affected by child benefit changes – in families where one parent is earning more than £50,000 a year they will no longer be able to claim the total amount of child benefit – and 700,000 would be hit by tax credit cutbacks.
Ms Sturgeon spoke to the Scottish Parliament Welfare Reform Committee as the Scottish Government attempts to put in place a system to manage the impact of changes.
She said progress was being hampered by a lack of inform-ation from the Department of Work and Pensions and a lack of appreciation that there was a "massive knock-on effect" on devolved administrations.
She said people on 'passported benefits' – such as free school meals and disabled blue badge parking – would be affected, with some losing the initial benefit that entitles them to another.
Alex Johnstone, Conserv-ative MSP on the committee, said the UK Government's aim was to make work pay.
Ms Sturgeon said: "We all want a system where work pays. One of my concerns is that while they say it is about making work pay it is working against that.
"A significant chunk of the changes will fall on people in work. With changes to Working Tax Credits, Child Tax Credits and benefits uprating people are going to find it harder.
"This is not a distinction between the strivers and the so-called scroungers the UK Government thinks it is. It will hit people already working hard.Many people who have 'passported' benefits are in work. If you are in a low-paid job, getting free school meals for your child is important."
Changes start this month with some people on higher incomes losing child benefit payments.
In April pilots to replace a range of benefits with a single Universal Credit payment begin. They will be extended nationwide starting in October.
Ms Sturgeon said the 1% cap on benefit rises was an actual 4% cut, adding: "I have never disagreed with the objective of making work pay, but the changes are running counter to those objectives."