The invention relates to a silicon-aluminum carrier containing two modified molecular sieves. The silicon-aluminum carrier includes a modified Y molecular sieve, a modified ZSM-23 molecular sieve, and amorphous silicon-aluminum. The modified Y molecular sieve adopted by the carrier is a deep dealuminated Y molecular sieve, which has the characteristics of integral crystal form, high silicon-aluminum ratio, low acid center density, high medium-strong acid proportion and abundant secondary pores, and is suitable to serve as the acidic cracking component of a medium oil type hydrocracking catalyst. The high specific surface and developed secondary pores not only promote exertion of the hydrogenation activity, but are also conducive to spread of the reaction product, the secondary pores are numerous, and the acid center density is low, so that the probability of excessive cracking and secondary cracking can be reduced. Therefore, the catalyst can have excellent medium oil selectivity, high silicon-aluminum ratio, small lattice constant and stable structure, and has very good stability.