Pung Chiv Kek, president of the human rights group Licadho, said that the election campaign did not bode well for the vote.
"We still have 13 activists killed, including the journalist of the opposition newspaper, so this sends a very negative message to the voter."
"We can hardly say that this election is free because there is still intimidation and physical abuse - this is the stick. The carrot is buying votes, building roads and schools.
"By using sticks and carrots, we are sure the ruling party will win a large majority."
Pung Chiv Kek told Al Jazeera that the CPP is expected to win because opposition parties have also not presented a significantly attractive vision to the Cambodian people.
"The opposition divide didn't manage to unify before the election, so their seats in parliament will be less."
She also denied that the ruling party was popular due to the country's economic success in recent years.
"The GDP [gross domestic product] seems to have increased, but look at the gap between the rich and the poor, more than 40 per cent of the poor live below the level of international standards."
In the absence of a credible opposition Pung Chiv Kek said Cambodia will have more problems "of land grabbing, evictions, corruption, impunity, no independence of the judiciary".
'CPP will win'
Talks between Thailand and Cambodia on Monday have failed to end a military stand-off over the disputed Preah Vihear temple on their border, recently listed by Unesco as a World Heritage Site.
|Sam Rainsy, left, an opposition leader and Hun Sen, right, the prime minister [AFP]
Hang Puthea, head of the election monitoring group Nicfec, said campaigning had been largely overshadowed by concerns over the temple.
"People are more focused on the border issue at Preah Vihear temple than on the election," he told AFP.
Boonsrang Niumpradit, Thailand's supreme commander, the result of the talks was to allow soldiers to stay in their current positions at the temple, but avoid any confrontation.
Hun Sen has accused Thailand of ignoring international law and threatening regional peace by sending troops into the disputed zone around the temple.
Poor track record
Chea Vannath, an independent political analyst, said: "There is no doubt that CPP will win the election."
At least 8.1m people are registered to vote at 15,000 polling stations, under the supervision of more than 13,000 domestic and international observers.
Previous polls held in Cambodia, have been hit by violence. Scores of people - mainly opposition supporters and activists - were killed or beaten in the run-up to elections in 1998.
Election monitors say political violence has diminished greatly compared to past polls, however, unequal access to the media is being criticised.
The main government controls almost all of Cambodia's broadcast media, while the CPP maintains a vast network in rural Cambodia, inherited from the party's communist days.
At least 35 per cent of Cambodia's 14m people live on less than 50 US cents a day.
However, economic growth has averaged about 11 per cent over the past three years, creating a sense of optimism in a country that recently emerged from decades of civil war in 1998.
Analysts say the main question going into the polls is whether CPP will be able to increase the 71 seats it already holds in the 23-member parliament.