Is there a contradiction between joining the party and going abroad?

There will be some impact, but the problem is not big. Just fill in the form, don't write party member. Unless you want to work in a foreign government department, such as the Intelligence Bureau, you won't mind whether you are party member or not. But if you fill in your name as party member, you will definitely have trouble getting a visa, and the people in the embassy will carefully examine it. Although there is no explicit stipulation to restrict party member from going abroad, the immigration officer will have misgivings when examining and signing, and there will be many things to consider. Maybe he will let you go to the Chinese Consulate General in Beijing for an interview and ask about your purpose of going abroad. If you are not a fool, don't write a form. In addition, if your parents are party member, you'd better not write it in the form, otherwise it will be very troublesome. If party member wants to go abroad, he must conceal China's party member identity when applying for a visa, and so must studying abroad. If you realistically recognize your China party member, the Japanese Embassy will not grant you a visa.