In order to further improve the security and efficiency of Number Theory Research Unit (NTRU)-type Multi-Key Fully Homomorphic Encryption (MKFHE) schemes, based on the prime power cyclotomic rings, the properties of the original decryption structure of NTRU-type multi-key fully homomorphic encryption were studied, and two optimization methods of multi-key homomorphic decryption structures were proposed. Firstly, by reducing the polynomial's coefficients, the "Regev-Style" multi-key decryption structure was designed. Secondly, the "Ciphertext-Expansion" multi-key decryption structure was designed by expanding the dimension of ciphertexts. Compared with the original decryption structure of NTRU-type multi-key homomorphic encryption scheme, the "Regev-Style" multi-key decryption structure reduced the magnitude of error, which was able to reduce the number of key-switching and modulo-switching when it was used in the design of NTRU-type multi-key homomorphic encryption scheme; the "Ciphertext-Expansion" multi-key decryption structure eliminated the key-switching operation, reduced the magnitude of error, and was able to process the ciphertext product of repeated users more effectively. The security of the optimized multi-key decryption structures was based on the Learning With Errors (LWE) problem and Decisional Small Polynomial Ratio (DSPR) assumption on the prime power cyclotomic rings, so these structures were able to resist subfield attacks well. Therefore, they can be used to design a more secure and efficient NTRU-type multi-key fully homomorphic encryption scheme by selecting appropriate parameters.