Cash saved would go to charities which boost young people's involvement in politics, Andrew RT Davies said.
From May, pay for the first minister will rise to £140,000 while other ministers will be paid £100,000.
Ahead of a policy speech in Cardiff, Mr Davies said his plan would save about £250,000 over a five-year term.
The party said it would revive the idea of a youth parliament for Wales.
Mr Davies was due to say in a speech in Cardiff on Thursday: "Wales should embrace organisations that encourage children and young people to get involved in the decision-making process and to support them in understanding their rights and responsibilities.
"And denying young people that opportunity to learn, to influence and to develop is all the harder, when - indeed - assembly members are set to benefit from a pay rise of their own.
"That's why a Welsh Conservative government would cut ministerial pay by 10% across the board and plough every penny of that funding into giving young people a voice - reviving support for a national children and young people's assembly for Wales."
In 2015, an independent panel's decision to give AMs a pay rise prompted criticism from all parties.
The assembly's remuneration board insisted higher salaries were justified given that Wales had more powers than ever before and the lure of better pay could also improve the calibre of candidates.
Mr Davies also planned to repeat calls for the assembly to take shorter holidays, meet more often and force ministers to answer "topical" questions without advance notice.
He will promise a Tory administration would introduce a "localism and citizenship bill", giving communities the right to buy community assets including shops and pubs, and introduce a cap on senior pay levels in local councils.
The Conservatives are also calling for the children's, older people's and future generations commissioners to be made accountable to the assembly as a whole, rather than the Welsh government.
A 10% pay cut for Welsh government ministers will be brought in if the Tories win May's assembly election, the party's leader in Wales has said.