Previous research initiated party effect would influence electoral result through resource mechanism, ideological mechanism, and individual characteristic mechanism. Besides, it can also be moderated by the general electoral environment. However, little research has comprehensively summarized the party effect mechanism under the constrained democratic system in Hong Kong. Accordingly, this paper presents analysis of a set of data including all candidates (N= 965) from Hong Kong Legislative Council (LegCo) since the first direct election in 1991. This research attempts to analyze how political party influence the LegCo election through what mechanisms. The results indicate that voting preference in LegCo still biased to pro-democratic candidates, while the pro-Beijing camp ensured their leading status by institutional guarantee. Specifically, party effect in Hong Kong LegCo is subjected to a complicated mechanism, tying to candidate’s ideological preference, rather than their affiliated party. Besides, candidates who owned the esteemed occupational orientation will be more likely to win. Moreover, the grand electoral environment significantly moderates the party effect in Hong Kong. The resource mechanism only reflects on the party size. Finally, the electoral advantage has gradually shifted towards pro-Beijing affiliation over time.