The invention provides an ECC(elliptic curve cryptography) coprocessor, which comprises a command/status register, a decoding control unit, a data register, a double-port SRAM(static random access memory), a point addition control unit, a point multiple control unit, a modular exponentiation control unit, a modular multiplication control unit, a modulo addition/subtraction control unit and a basic operation unit. The ECC coprocessor realizes functions of big integer modular multiplication, modulo addition/subtraction, modular exponentiation control and elliptic curve point addition/multiple operation and provides the same to the external. Since coordinates of the elliptic curve points in external interfaces for point addition and point multiple operations are projection coordinates or mixed coordinates, the ECC coprocessor is capable of supporting an external controller to realize point multiple operations in different types flexibly.