In 1946, Cheng Qiang led his troops to take over the Harbin Puppet Manchukuo Police Department and served as the director of the Public Security Bureau. Harbin at that time was facing double pressure: the Kuomintang entrenched in Changchun could attack Harbin at any time, and hidden enemy special organizations, bandits, Japanese puppet personnel and even hooligans were waiting for an opportunity to cause chaos. Internally, public security cadres came from all corners of the country, with different working ideas and methods, and often had differences when encountering specific problems. The trade unions and farmers' associations were also arguing about who was the leader of urban management. The city leadership lacked experience in managing large cities, etc., all of which put great pressure on Cheng Qiang and his comrades. The Kuomintang successively sent senior spies and agents who had received special training in the United States to sneak into Harbin. Cheng Qiang gathered the forces of all parties in the Public Security Bureau and relied on the grassroots masses to prevent the enemy's conspiracies one by one. In order to stabilize social order, a neighborhood committee was established to improve the management of foreign residents in the city, and to abolish brothels, opium dens and casinos. The internal ghosts lurking in our Public Security Bureau were cleared and the assassination of General Li Zhaolin was solved.