Hello Dinghui, this is an easy one. You can remember contrOversy, because controversial things always makes people gasp and say, "OH!". Contr O! versy. ( ﾟoﾟ)

You could try pronouncing it an alternative way? https://www.youtube.com/watch?v=RH9ArWGgG0s is a valid way, and emphasises the 'oh' sound in the middle.

Try learning it by remembering the 'root word' ('词根') CONTROVERSY = CONTRO + VERS + Y where CONTRO means 'against'. The root word CONTRA, COUNTER and CONTRO come from Latin 'contra' meaning 'against'. Similarly (just copied): country (n.) mid-13c., "district, native land," from Old French contree, from Vulgar Latin *(terra) contrata "(land) lying opposite," or "(land) spread before one," from Latin contra "opposite, against" (see contra-). Sense narrowed 1520s to rural areas, as opposed to cities. Replaced Old English land. As an adjective from late 14c. First record of country-and-western music style is from 1942. Country club first recorded 1886. Country mile "a long way" is from 1915, American English. countermand (v.) early 15c., from Old French contremander "reverse an order or command" (13c.), from contre- "against" (see contra-) + mander, from Latin mandare "to order" (see mandate (n.)). Related: Countermanded; countermanding. encounter (n.) c. 1300, "meeting of adversaries, confrontation," from Old French encontre "meeting; fight; opportunity" (12c.), noun use of preposition/adverb encontre "against, counter to" from Late Latin incontra "in front of," from Latin in- "in" (see in- (2)) + contra "against" (see contra). Modern use of the word in psychology is from 1967, from the work of U.S. psychologist Carl Rogers (1902-1987). Encounter group attested from 1967. contravene (v.) 1560s, from Middle French contravenir "to transgress, decline, depart," from Late Latin contravenire "to come against," in Medieval Latin "to transgress," from Latin contra "against" (see contra) + venire "to come" (see venue). Related: Contravened; contravening. counterbalance (v.) 1570s, from counter- + balance (v.), in reference to scales. Figurative use dates from 1630s. As a noun, from c. 1600. countryside (n.) mid-15c., literally "one side of a country" (a valley, a mountain range, etc.), from country + side (n.); hence, "any tract of land having a natural unity" (1727).

Well, a word in the middle of controversy is trove, so you could make a sentence with trove. "The investigating committee discovered a trove of controversy" or something.

I agree with Gary. If you pronounce 'controversy' the traditional way, stressing the second syllable and reducing the third syllable to a schwa, you will hear that there's an 'o' in the middle. Not many words have alternative options for pronunciation, but this one does. And in this case, it'll help with your spelling. But the spelling of one word - and not the commonest of words, either - is a fairly minor issue, isn't it? You might do better to concentrate on your basic grammar. Nobody will mind too much if you get the odd 'o' or 'a' wrong, but it does matter if you make mistakes with your key verb constructions. "I always misspelling...."?? Ouch. Your profile says that your level of English is advanced, so you shouldn't be making beginner-level grammar errors. I hope that was just a typo.