Chang Chien was born in 1853 in Haimen Kiangsu and died in 1926 in Nant’ung Kiangsu. Although for a couple of years Chang Chien had been extraordinarily enthusiastic in the promotion of a constitutional monarchy, he changed from a constitutional monarchist to a republican within one month or so after the 1911 Revolution. Why did he change? This is a significant topic for discussion. So far lots of scholars have done research on this topic, however, the answers to this question have not been fully exploited yet. My finding in this paper contends that though reasons leading to Chang Chien’s conversion were complicated, the main reason should be attributed to his belief in industry, education and self-government were able to be achieved under whether a constitutional monarchy or a republic. The second reason for his shift should be attributed to his pragmatic attitude to face situation, and the third reason should be due to his disappointments with the Ch’ing government. This paper is also to explore Chang Chien’s decisive role in the North-South negotiation from December 1911 to February 1912 leading to the abdication of the Ch’ing government under certain kind of concession in exchange for the support of Yuan Shih-k’ai as the president of the republic.