A method of controlling a fuel injection quantity using a lambda sensor may include performing a lambda deviation learning mode by controlling a lambda deviation, due to a difference between a lambda model value and a lambda sensor measurement value, by a controller during engine combustion in which an engine RPM and a fuel injection quantity are detected, wherein, in the lambda deviation learning mode, a learning map is learned and is then updated by setting a fuel correction quantity depending on the lambda deviation as a learning value, and a fuel injection quantity is determined, in consideration of the fuel correction quantity depending on an RPM and a fuel quantity based on the updated learning map, and is output as an output value, so that the output value is applied to feedback control for a next fuel injection quantity.