It was analyzed how a firm's decision to invest in a new technology would effect on the expectation net proceeds of the firm with the new technology when the cost of carrying out this technology was decreased. The optimal speed of the innovation an emerging technology under the conditions that technological circumstance changed quickly was studies. On the assumption that technology progress follows the c process, three investment strategies for using technology by firms were analyzed. The optimal innovation speed was acquired by comparing the expectation net proceeds of the firms with the technology. The effects of several important parameters on the expectation net proceeds were showed through the numerical illustrations.