Advances in quantum computation threaten to break public key cryptosystems that are based on the difficulty of factorization or the difficulty of discrete logariths, although, no quantum algorithms have been found to be able to solve certain mathematical problems on non-commutative algebraic structures up to now. The proposed new quasi-inverse based cryptography scheme is vulnerable to a linear algebra attack based on the probable occurrence of weak keys in the generation process. In this paper, we illustrate that two of the quasi-inverse based cryptography are vulnerable to a structural attack and that it only requires polynomial time to obtain the equivalent keys for some given public keys. In addition, we conduct a detailed analysis on attack methods and provide some improved suggestions on these two schemes. Advances in quantum computation threaten to break public key cryptosystems that are based on the difficulty of factorization or the difficulty of discrete logariths, although, no quantum algorithms have been found to be able to solve certain mathematical problems on non-commutative algebraic structures up to now The proposed new quasi-inverse based cryptography scheme is vulnerable to a linear algebra attack based on the probable occurrence of weak keys in the generation process. In this paper, we illustrate that two of the quasi-inverse based cryptography are vulnerable to a structural attack and that it only requires polynomial time to obtain the equivalent keys for some given public keys. In addition, we conduct a detailed analysis on attack methods and provide some more suggestions on these two schemes.