每个月都要买些新书用英语怎么说

"Buy new books every month" 可以说成 "purchase new literature on a monthly basis"。

"Purchase" 是买的意思，"literature" 是书籍的意思，"on a monthly basis" 是指每个月。

例句：

I always purchase new literature on a monthly basis to keep my mind fresh. (我每个月都会买一些新书来保持头脑清新。)
She buys new books every month to keep up with the latest trends in literature. (她每个月都会买新书来保持对文学的最新趋势的了解。)