Kim Jong Il put forward the Juche-oriented idea and theory on the party building and successfully applied them, strengthening the WPK into the militant and revolutionary party which forms a harmonious whole with the popular masses.

He made public the work "Let Us Strengthen Our Party into the Party of Comrade Kim Il Sung Forever" on June 20, Juche 53 (1964). The work referred to the historic root of the WPK and clarified the idea and theory for strengthening the WPK into the party of President Kim Il Sung forever.

In his works including "On Some Immediate Tasks of Party Ideological Work for Modeling the Whole Society on Kimilsungism" and "Let Us Establish the Monolithic Ideological System More Thoroughly Throughout the Party and Society" he formulated the revolutionary idea of Kim Il Sung as Kimilsungism and proclaimed the modeling of the whole society on Kimilsungism as the supreme programme of the WPK and gave perfect answers to the theoretical and practical problems arising in building the working class party.

In his works such as "People's Army Should Take the Lead in Realizing the Cause of Our Party" and "Commanding Officers of the People's Army Should Become Genuine Kimilsungists" he set forth the tasks for the people's army to preserve the attribute as the army of the leader and the party and energetically led the army to successfully discharge this mission and duty.

"The Historical Lesson in Building Socialism and the General Line of Our Party", "The Songun-based Revolutionary Line Is a Great Revolutionary Line of Our Era and an Ever-Victorious Banner of Our Revolution", "Songun Politics of Our Party Is an Effective Socialist Political Mode" and other works clarified the idea of taking hold on the Songun politics as almighty treasured sword for the victory of the revolution.

Under his leadership the WPK developed into a revolutionary party which remains unfailingly loyal to the idea and leadership of the leader and has the strong sense of organization and discipline and an invincible party with solid mass foundation.