The core of choosing a secure elliptic curve for elliptic curve cryptosystems is the calculation of the order of a randomly selected elliptic curve. It is known that SEA (Schoof Elkies Atkin) algorithm is recently the most efficient method to calculate the orders of elliptic curves over Fp. Isogeny cycles method made by Morain is an important local optimized technique to improve SEA algorithm. In this paper, isogeny cycles method is enhanced, and a scheme of more optimal combination of the various techniques in SEA algorithm is provided.Furthermore,some discussions are made on how to speed up the selection of elliptic curves with prime order,and an efficient implementation of SEA algorithm overF_p is described.