Face of Nation : Welsh band the Manic Street Preachers will perform at the castle on Saturday night, before legend Paul Weller entertains crowds on Sunday night.
Castle Street and North Road will be closed for about 30 minutes, to give people chance to leave the castle.
The castle has a capacity of more than 10,000 people.
The Killers played Cardiff Castle in their Summer Sounds series the night before they headline the main Pyramid stage at Glastonbury on Saturday night.
The weather forecast has said it will be warm with plenty of sunshine, but there is the chance of the odd scattered showers and Sunday will be a cooler and breezier day.
The Killers paid tribute to BBC presenter Rachael Bland, who died at the age of 40 almost two years after being diagnosed with breast cancer.
Her husband Steve Bland said the dedication was “unbelievable”.
Mr Bland had sent a message asking if they would dedicate a song to his late wife, who was the band’s “biggest fan”.
He said: “Even when her cancer made her so very ill your music brought her to life. She died in September.
“On Friday we’re coming to see you in her home city Cardiff. A song dedication would mean the world.”
