积极财政政策是指政府通过增加财政支出和减少税收来刺激经济活动的一种政策。当一个国家采取积极财政政策时，股票市场通常会受到积极的影响，股价也会上升。这种现象可以通过以下几个方面来解释。

首先，积极财政政策会促进经济活动的增长。当政府增加财政支出时，例如投资基础设施建设、教育、医疗等领域，这会带动相关产业的发展，刺激经济增长。经济活动的增加将直接增加企业的盈利机会，使得投资者对市场的前景更加乐观，从而推动股票价格上涨。

Firstly, expansionary fiscal policy promotes economic growth. When the government increases fiscal expenditure, for example, in infrastructure construction, education, healthcare, and other sectors, it stimulates the development of related industries and drives economic growth. The increase in economic activity directly leads to more profit opportunities for businesses, making investors more optimistic about the market outlook and driving stock prices higher.

其次，积极财政政策可以提高消费者的购买力。政府的财政支出通常会刺激经济的需求侧，进而增加人民的收入。当人们的收入增加时，他们更有可能消费更多的商品和服务。这将直接影响到一些企业的销售额和利润。当市场对企业的销售前景更加乐观时，股票价格也会随之上涨。

Secondly, expansionary fiscal policy can enhance consumers' purchasing power. Government fiscal expenditure usually stimulates the demand side of the economy, consequently increasing people's incomes. When people have higher incomes, they are more likely to consume more goods and services. This directly impacts the sales revenue and profits of certain businesses. When the market becomes more optimistic about a company's sales prospects, stock prices also tend to rise.

此外，积极财政政策还可以改善企业的盈利能力。政府通过减少税收来刺激经济发展，降低企业的税负。较低的税负意味着企业可以获得更高的利润。当企业的盈利能力提高时，投资者对这些企业更加青睐，从而推动股票价格上升。

Furthermore, expansionary fiscal policy can improve business profitability. The government stimulates economic development by reducing taxes, thereby reducing the tax burden on businesses. A lower tax burden means that businesses can generate higher profits. When a company's profitability increases, investors are more inclined to favor these companies, thus driving stock prices higher.

综上所述，积极财政政策通过促进经济活动的增长、提高消费者的购买力以及改善企业的盈利能力等方面，对股价的上升起到积极的作用。投资者往往会对经济发展预期乐观，从而促使股票市场的反应。然而，需要注意的是，财政政策的实施也可能带来一些负面影响，如通货膨胀和债务累积等问题需要及时监控和调整。

In conclusion, expansionary fiscal policy plays a positive role in driving up stock prices through stimulating economic activity growth, enhancing consumers' purchasing power, and improving business profitability. Investors tend to be optimistic about economic development expectations, thus influencing the reaction of the stock market. However, it is important to note that the implementation of fiscal policy may also bring some negative impacts, such as inflation and accumulating debt, which need to be monitored and adjusted in a timely manner.