Abstract: According to the problem of big rock blocks, high strength in collapse column which leads to coal face can not directly passing collapse column, we proposed that using hydrochloric acid softening method at Tang'an mining 3405 fully mechanized coal face to directly passing collapse column and it carried out successfully. The experiment showed that mechanical strength of sandy mudstone was exponential law change with hydrochloric acid solution concentration; the mechanical strength of sandy mudstone was decreased of negative logarithmic law with the soak time of hydrochloric acid solution increased; with the increased of hydrochloric acid solution concentration, its porosity increased, yield point was obvious and plastic raised.