Quantum image encryption is an emerging technology for efficiently protecting visual information. A quantum block image encryption scheme is designed based on quantum Arnold transform (QArT) and lately proposed sine chaotification model (SCM) in this paper. Firstly, in order to flexibly manipulate image blocks, a quantum block image representation (QBIR) model for block image is proposed, which encodes pixel gray values and position information of image blocks into two entangled qubit sequences. Then, QArT is applied to scramble the positions of image blocks. The final ciphertext image is obtained by quantum XOR operations, which is completed with a pseudorandom sequence generated from SCM. The introduction of SCM dramatically enlarges the key space to resist brute-force attack. Moreover, the generated sequence is dependent on the original image to resist the chosen-plaintext attack. The main quantum circuits are given and numerical simulation results demonstrate that the proposed quantum image encryption scheme is valid and reliable for quantum image protection in terms of security and computational complexity.