To improve the TAC resistance to ciphertext and selective plaintext attacks, a novel security arithmetic coding scheme based on M-ary symbol is proposed.It combines data encryption with compression.The modified arithmetic coding methodology changes the encoding interval and codeword of TAC by using an encryption key to alter the symbols orders in the encoding interval.Simulations both on static and adaptive model show that M-SAC can obtain higher SER than BRAC when decoding with a wrong key.The proposed encryption algorithm satisfies highly security without loss of compression efficiency, which has strong resistant to ciphertext and selective plaintext attacks.