JAMES SPADER is winning raves on the new NBC hit “The Blacklist,” but he’s a TYRANT on the set, an insider says.

The Emmy-winning actor is feuding with his sexy young co-star – blasting her for blowing her lines – and he’s freaking out others with his weird behavior.

Spader plays Ray Reddington, a ruthless criminal mastermind who, for mysterious reasons, has come out of hid­ing to assist the FBI on condition that he deals only with young agent Liz Keen, played by Megan Boone.

In one ep, Spader had to deliver complicated dialogue over and over for 12 frustrating takes because Megan couldn’t keep up.

“It’s a matter of experience, and it shows,” said an insider.

 “James should be cutting her a break, but he’s a big bully.”

Spader, 53, first drew atten­tion in Brat Pack films such as “Pretty in Pink” and later starred in the 1989 movie “Sex, Lies and Videotape.”

More recently, he’s played eccentric characters on TV shows, includ­ing “The Practice” and “Boston Legal.”

 While his career spans 35 years, Megan, 30, is best known for appearing on the short-lived “Law & Order: Los Angeles.”

“James is frus­trated, but the show is such a hit that producers aren’t about to change anything,” said the source.

And there’s little they can do about him sending chills through cast mates by staying in his creepy character even when the cameras aren’t rolling.

“He stares right through the other actors and speaks to them in the same unnerving way his character talks,” said the source.

“It’s like dealing with a real psychopath”.