The invention discloses a reinforcement cage and steel formwork integrated transverse assembly method. The reinforcement cage and steel formwork integrated transverse assembly method comprises the steps: 1, an assembly platform is set up; 2, a first L-shaped steel formwork is hoisted; 3, a reinforcement cage is hoisted; 4, a second L-shaped steel formwork is hoisted and fixedly connected with thefirst L-shaped steel formwork; 5, designated steel bars in the reinforcement cage are selected and marked; 6, a main bar connecting sleeve is mounted and connected with main bar connecting pipes; 7, ajack is inserted and fixedly connected with a steel formwork top sealing plate; and 8, the reinforcement cage and a steel formwork are fixed. Through splicing of the first L-shaped steel formwork andthe second L-shaped steel formwork, the reinforcement cage is placed in the steel formwork and fixed, the subsequent main bar connecting pipes are mounted advantageously by marking the designated main bars, through cooperation of the jack, the main bar connecting pipes, the main bar connecting sleeve and a main bar fixing sleeve, the reinforcement cage and the steel formwork are fixed into a whole, later overall hoisting of the reinforcement cage and the steel formwork is convenient, and thus the construction process is simplified.