Using NCEP/NCAR daily reanalysis dataset and Guangdong daily precipitation from 1961 to 2017, by selecting and classifying the rainstorm processes in the warm sector in Guangdong only caused by South China Sea monsoon trough without the frontal system, the temporal and spatial distribution characteristics of different types of monsoon trough rainstorm processes and their relationship with atmospheric low-frequency oscillations are studied, focusing on revealing atmospheric circulation field evolution characteristics in phase of quasi-biweekly oscillations and the sources of low-frequency signals with strong southwest monsoon jet-type monsoon trough rainstorm process, by the methods of synthetic analysis, wavelet analysis and Lanczos filter. The strong southwest monsoon jet type monsoon trough rainstorm process accounted for 53.1% of the total cases, mainly occurring in the three major rainstorm centers (Yangjiang-Yangchun-Enping, Haifeng-Lufeng-shanwei, Longmen-Fogang) along the coast and inland of Guangdong. The other three types of monsoon troughs rainstorm process (strong southwest monsoon convergence type, southeast monsoon disturbance type, tropical cyclone away type) mainly occurred in the two major rainstorm centers along the coast of Guangdong and on both sides of the Pearl River Estuary. The monsoon trough rainstorm process mainly exhibit quasi weekly (5-8 days) and quasi biweekly (10-28 days) oscillations but less 32-65 days oscillations. During the intermittent-start-peak-weak period of strong southwest monsoon jet-type monsoon trough rainstorm process，the low-frequency signal not only originates from the southeastward-propagatian of the quasi-barotropic low-frequency wave train consisting of a series of anomalous anticyclones and cyclones from Western Europe to Northeast Asia，but also originates from the northwestward propagation of low-frequency cyclones in the tropical western Pacific of southeast Philippines in the middle and lower troposphere. They made the South Asian High move westward from Bangladesh to Pakistan, the western Pacific subtropical high gradually strengthened and extended northwestward, from Balkashi Lake to Baikal lake ,central and eastern China is controlled by low frequency anticyclonic circulation or high pressure ridge in intermittent period gradually turning into low frequency cyclonic circulation or upper trough in peak period. In South China, the upper-air divergence gradually increases and reaches the strongest, as the strong northeasterly at the southeast side of the low-frequency anticyclonic circulation gradually changes to the strong westerly from the bottom of low-frequency cyclonic circulation which controls the North China and South of the Yangtze, and the northwesterly from periphery of low-frequency anticyclone which controls the Indian Peninsula-Northwest South China Sea. The middle and lower layers are gradually controlled from the low frequency anticyclone circulation or high pressure ridge to the strong southwesterly which comes from the north of the low frequency anticyclone which controls the central and northern South China Sea and the Bay of Bengal, the strong low-frequency cyclonic circulation and positive vorticity are formed over Southwest China, South of the Yangtze and South China ,when the strong southwesterly are blocked by the low-frequency anticyclone circulation over Northeast Asia, Japan and the southwestern Pacific. The Sea level pressure gradually changed from a weak uniform pressure filed to a closed low pressure extending northwards from the Beibu Gulf , the South China Sea monsoon trough lifts northward and strengthens, making the strong southwest monsoon jet-type monsoon trough rainstorm from the intermittent to peak period. These are beneficial to medium-extended-range forecast of monsoon trough rainstorm processes.