Kate Jackson -- one of the original stars of "Charlie's Angels" -- claims she's now in "financial ruin" ... and she's blaming it all on a guy she met through Farrah Fawcett.

The 61-year-old actress has fired off a lawsuit against her financial advisor -- claiming the dude has screwed her out of more than $3,000,000.

According to a lawsuit filed in L.A. County Superior Court, Jackson claims Fawcett's former business manager, Richard B. Francis, knew about Kate's "extremely close relationship" with Farrah and used that information to get Kate as a client. 

In the docs, Jackson claims Francis told her she was worth roughly $5.4 million -- and she could live off of the interest from her accounts ... at least $300,000 per year.

But Jackson claims she was sorely misinformed and discovered she was actually worth considerably less -- only about $3 million. Jackson claims she learned the truth about her finances when she agreed to buy a home in 2008.

According to the docs, Francis pressured Jackson into buying a home for $2,011,000 in an area he called the "Golden Strip" in Santa Monica ... promising the property would never lose value.

Kate claims Francis knew she couldn't afford the home, but he drained her savings account in order to pay for it anyway. Kate also claims Francis knew she was grossly overpaying for the property.

Kate is now suing for more than $3,000,000 -- claiming she has "suffered financial ruin at the hands of the very person she entrusted with her finances."

Francis says he's been in the business for 50 years and has an impeccable record with several celebrity clients.  He added, "This case will end at the deposition stage. It will never go to court."