Origin of Chinese National Day

It's been 60 years. So much has happened in the past decades in China. It would be concluded by a certainly magnificent military parade in 3 hours' time.

But does anyone know why the communist party established the new regime on this day?

You may say, there is no reason why. Because they felt they were ready on that day. Yeah, you are right. But communist troops had occupied Beijing since Jan 31 without fighting. Why didn't they pronounce their success earlier?

You may also say, because they didn't announce until they finisht the war. But on Oct 1, 1949, 50% of Chinese territory is still either under KMT control (southern and southwestern), or controlled by local government (Tibet, Xinjiang). We could well say that the war was far from over (which was verified by the division along Taiwan strait later).

I believe, as the tradition of communism, symbolism is always important. The first communist country, Soviet Union was established during October Revolution (though it's November 7 on Gregorian calender because Russian Orthodoxy used a different calender). As a continuation of great communist campaign, being established on October is a important.

Also, there was a negotiation with Soviets underway. Stalin wanted to continue controling Mongolia, Xinjiang and Manchuria. As a nationalist, Mao wouldn't allow this kind of humiliation for the new regime. The negotiation was so fierce that Soviet embassy even moved with KMT government to Guangzhou (the very south of the country) while the American ambassador refused to move and wanted to talk to new regime. The bargaining finally resulted in independence of Mongolia for the return of Xinjiang and Manchuria but a lease continued in Dalian. Without ensuring the Soviet support, any proclamation would be premature (Soviet established diplomatic relations with China on Oct 2, before any other country).

Any delay after October 1 would be risky because a cold snowy winter day wouldn't be a good one for a communist regime to showcase its power in a military parade (which was a problem for Soviet leader to stand in bleeding cold Red Square for several hours, which was a touch job for elderly Soviet politburo members).