You can use traffic analyzing tools like alexa to find an approximate traffic to your competitor , never expect the accurate result using these tools.
There are some tools that can provide you with some competitive analysis such as Comscore, KeywordDiscovery competitive Intelligence, and Hitwise.
I'd say it's pretty near impossible to find out traffic from a site you don't own. You could try using Alexa for example but for the average website with Alexa > 400,000 or so, the directory owner can skew the traffic figures greatly by installing the Alexa toolbar and clicking around their own website every day. Only when you get below 100,000 does Alexa seema more accurate representation.
Like stated above, you won't be able to get a 100% accurate review of your competitors, but sites such as Alexa & Websiteoutlook can give you a general idea.
that seem to be little true if some one is saying this is perfect answer then let me know i exactly do not know if its right