Hi Afzal and welcome to the forum :)
Alipay is a division of Alibaba itself and an extremely popular payment gateway used in China. Now I have no personal experience using the service, but I know it dominates that market space within China, just as PayPal dominates that space in most western countries.
Is it safe?
From everything I know about Alipay, it is certainly considered to be a very safe payment method. Very large US retail brands like Macy's and Bloomingdale's offer the payment service for customers shopping from China. So despite not being so well known outside of China, it's the big name in town within China.