In many online social media systems, like other social network, because of social influence, ideas, modes of behavior and new technologies can diffuse through the network like a epidemic. However, different social tie strength between users will cause different speed and different extension of information diffusion. Users with strong social ties exhibit information diffuse more easily than those with weak ties. Therefore, researchers are very interested in identifying social ties in information diffusion. Generally it is difficult to identify the social ties, because it is latent. But there are some factors can induce it. In this paper, we presented a technique to measure the correlation between social ties and reciprocity, and applied it to real-world dataset on Sina Microblog. Results showed that there was a significant correlation and strong tie existed in reciprocal links in this system. Then we can predict the social ties easily by reciprocity.