The fundamental mark that distinguishes the old and new democratic revolutions is that the most striking difference between the two is the difference in the leading class of the revolution. The leading class of the new democratic revolution is the proletariat, while the leading class of the old democratic revolution is the bourgeoisie. 
The new democratic revolution refers to the period from the May Fourth Movement in 1919 to the founding of the People's Republic of China in 1949, led by the proletariat and led by the masses of the people, mainly opposing imperialism, feudalism and bureaucratic capitalism. The Chinese revolution at this stage was anti-imperialist and anti-feudal in its thoroughness, and at the same time it had a broad mass base and the strategic character of the national united front. At this stage, the proletariat became the leading force of the revolution, united with the peasant class and the other petty bourgeoisie against imperialism and feudalism. 
In contrast, the old democratic revolution refers to the revolutionary struggle of the Chinese led by the bourgeoisie from 1840 to 1919 against foreign invaders and their own exploiters. The revolutionary struggle at this stage was mainly aimed at opposing the oppression of imperialism and feudalism and overthrowing the feudal rule of the country. However, due to the weakness and compromise of the bourgeoisie, the revolution was ultimately unable to accomplish its anti-imperialist and anti-feudal tasks. 
To sum up, the fundamental mark that distinguishes the old and new democratic revolutions is the difference in the leadership class of the revolution. The new democratic revolution was led by the proletariat, while the old democratic revolution was led by the bourgeoisie.