As an important delegation technology, proxy signature allows an original signer to delegate her signing capability to a proxy signer and the proxy signer can produce a signature on behalf of the original signer. At present, the length of proxy signature is a sum of lengths of two signatures in most of proxy signature schemes. It limits some applications for proxy signature. In this paper, we propose an efficient short proxy signature scheme without random oracle model based on Zhang et al.'s signature scheme. And the scheme is proven secure in the standard model and the security of the scheme is related to the k + 1-Square Roots Assumption. Compared with Huang et al.'s scheme, our scheme has several advantages over Huang et al.'s scheme in terms of the size of public key and computational costs of generation and verification of proxy signature. It is very suitable for mobile device.