Proxy authorization signature is essential to electronic commerce and other electronic transaction. This paper analyzed the security threats of present proxy authorization signatures and the basic principles of proxy signature together with its superiority in electronic transaction application. We present a conditionally anonymous proxy authorization signature scheme with forward security. The identity blinding and identity tracing algorithm enable the proxy signer to be conditionally anonymous for secrecy protection and authorization supervision; the scheme renders effective supervision on signature generating and authorization, avoids the misuse of proxy entrusting and identity tracing, prevents generalized signature forgery, coalition attack and intruder-in-middle attack. We also present an application case of the proxy authorization signature scheme in electronic commerce, it further justify the schemepsilas brevity, security, high efficiency regarding its application in such circumstances as with restricted computation ability, integrated space and limited bandwidth yet requiring for high-speed operation.