1. A mass spectrometric analyzer, comprising: electrostatic reflectors or electrostatic deflectors, enabling pulsed ions to be analyzed to move periodically for multiple times in an ion flight region, forming time focusing in portions of the ion flight region thereof, and forming an confined ion beam; a plurality of tubular detectors disposed in the portions of the ion flight region in which the time focusing is formed, and arranged in series along an axial direction of the ion beam, for picking up image currents when the ions pass through the plurality of tubular detectors; a low-noise electronic amplification device electrically connected to the tubular detectors, for detecting the image currents picked up by the plurality of tubular detectors differentially to acquire differential image current signals; and a signal processing device, for converting the image current signal into a mass spectrum.