1. A contrast imaging method based on a wide beam, comprising steps of: (1) constructing microbubble mother wavelets of phase 0/180 for a wide beam contrast imaging, according to a Herring-Trilling microbubble oscillation equation modified by Morgan model; (2) automatically emitting wide beam radio frequency (RF) signals, and receiving the wide beam RF signals which are reflected back by an object, by ultrasound array transducers; processing the wide beam RF signals of phase 0/180 which are received by the ultrasound array transducers, with a wavelet correlation analysis based on the microbubble mother wavelets obtained by the step (1); extracting a maximum wavelet correlation coefficient at an optimal wavelet transform scale; and constructing a pulse inversion microbubble wavelet transform (PIW) images matrix; and (3) constructing a pulse inversion sum squared differences (PISSD) thresholds matrix, determining decorrelation thresholds of the PIW images matrix obtained by the step (2), and obtaining a pulse inversion microbubble wavelet transform sum squared differences decorrelation (PIWSSD) image of the wide beam contrast imaging.