1. The number of master's students in China is increasing now, but the number of doctoral students is strictly controlled. Each doctoral supervisor may only take a few students, so it is natural to recruit the best students with the strongest scientific research ability. The screening process is strict, the admission requirements are high, and it is very difficult to get a doctorate.

2. Postgraduates applying for postgraduate entrance examination need to produce two or three papers and publish them in core journals with high recognition. The requirements for quantity and quality are relatively high, but many masters' academic achievements can not meet the requirements, so they are not eligible to apply.

3. Taking the unified examination is also an opportunity to read a PhD, but the number of places is small, the examination is difficult, and the English level is high. Moreover, it is even more difficult to achieve the corresponding standards in academic performance than to directly apply for a doctorate.